WHO ARE YOU TO (continually) JUDGE THE SERVANT OF ANOTHER: su tis ei (3SPAI) o krinon (PAPMSN) allotrion oiketen: (Ro 9:20; Acts 11:17; 1 Corinthians 4:4,5; James 4:11,12)

The “you” (su) is first in this sentence (emphatic position) which serves to place emphasis on this pronoun. It's as if Paul is saying  “as for you, who are you, etc.”

Judge (2919) (krino) primarily signifies to distinguish, separate or discriminate and then, to distinguish between good and evil, right and wrong, without necessarily passing an adverse sentence, although that is often what is usually involved. The present tense indicates this is a continual action.

Servant (3610) (Oiketes from oíkos = dwelling, home) designates a household slave, one holding closer relations to the family than other slaves. He is one of the household of the “family.” It is to his own master that the servant is responsible, not to "you".

J Vernon McGee has a pithy comment (as usual)...

Paul asks, “What right have you to judge another man’s servant?” What right have you, Christian friend, to sit in judgment on another Christian’s conduct when it involves something that is questionable? Are you God? Is that person accountable to you? Paul says, “He is not accountable to you. He is accountable to God. He is going to stand before his own Master.” Can you imagine being a dinner guest in someone’s home) and the servant brings in cold biscuits. You say to the servant, “What’s the big idea of bringing me cold biscuits?” And you chide—in our common colloquialism, bawl out—the servant! May I say to you, there would be an awkward silence in that home. That person is not your servant. Maybe she should not have served cold biscuits, but it is not your place to say so. I have a notion that the lady of the house will go back to the kitchen and will tend to the matter. Now maybe you disapprove of my conduct in one of these doubtful areas. I don’t have to account to you; you are not my master. I am responsible to Jesus Christ. He is my Master.' (McGee, J. V. (1997, c1981). Thru the Bible commentary. (Vol. 4, Page 741). Nashville: Thomas Nelson)

TO HIS OWN MASTER HE STANDS OR FALLS: to idio kurio stekei (3SPAI) e piptei (3SPAI) : stathesetai (3SFPI):

The first reason why you must not look down on the weak or judge or condemn the strong is because it is not your responsibility to change your brother in this area. You are not his master. He is not your servant. We are not responsible for one another's conduct in this area. Such responsibility is not defined in the Scriptures. This is an open area that each one has to decide before God, and, therefore, we have no responsibility to change each other and no authority to do so. He is not your servant, Paul says; the Lord chose him. The Lord, then, is the one responsible to change him. The Lord chose him without asking you or me

AND STAND HE WILL, FOR THE LORD IS ABLE TO MAKE HIM STAND: de dunatei gar o kurios stesai (AAN) auton: (3; 11:23; 16:25; Deuteronomy 33:27-29; Psalms 17:5; 37:17,24,28; 119:116,117; John 10:28-30; Romans 8:31-39; Hebrews 7:25; 1 Peter 1:5; Jude 1:24) (Isaiah 40:29)

 In spite of your sharp criticisms of one another. NLT is a good paraphrase & brings out Paul's idea well "Who are you to condemn God's servants? They are responsible to the Lord, so let him tell them whether they are right or wrong. The Lord's power will help them do as they should."

Ray Stedman comments that....:

The thing Paul brings out (V4) is that the man under consideration is being changed. He is on his way to standing. He will stand, Paul says. Stand, of course, means that he will be straightened out if he is doing wrong in this area. If it is really wrong, God will straighten him out and it is not up to you to do it. This is why I enjoy so much that little pin that Bill Gothard gives out with the letters PBPGINFWMY, i.e.,

"Please be patient, God is not finished with me yet."

ONE MAN REGARDS (judges) ONE DAY ABOVE ANOTHER: Os men (gar) krinei (3SPAI) hemeran par hemeran: (Galatians 4:9,10; Colossians 2:16,17)

"Again, one man thinks some days of more importance than others" (Phillips)

"In the same way, some think one day is more holy than another day" (NLT)

Though it was no longer required by God, the weak Jewish believer felt compelled to observe the Sabbath and other feast days associated with Judaism (Gal 4:9-10, see notes on Colossians 2:16-17). On the other hand, the weak Gentile might want to separate himself from the special days of festivities associated with his former paganism because of its immorality and idolatry.

Read this example of a "weaker" brother who regarded one day above another (and it helps one understand that a "weaker" brother is not necessarily one who is not spiritually mature):

In 1924 Eric Liddell, the "Flying Scotsman" was the fastest man in world in 100 meters. For months Eric Liddell trained with the purpose of winning the 100-meter race at the 1924 Olympics in Paris & indeed most sportswriters predicted he would win. Then Eric learned the qualifying heats were scheduled for Sunday. This posed a problem: Eric believed that he could not honor God by running on the Lord's Day. He simply said "I'm not running on a Sunday" & even said "no" to Prince of Wales, all because he regarded "one day above another".  Eric didn’t make a big deal about it and shout his convictions from the rooftop so people would see how pious he was. Nevertheless his fans were stunned by his refusal. Some who had praised him now called him a fool. But Eric stood firm in his convictions and did not go against his conscience (Ro 14:6 "he who observes the day, observes it for the Lord" & 14:23 "he who doubts is condemned if he (runs on Sunday), because his (running) is not from faith; and whatever is not from faith is sin") . Many thought it was completely in character for Eric & a lot of the athletes were quietly impressed by it. They felt that here was a man who was prepared to stand for what he thought was right, without interfering with anyone else, and without being dogmatic. That's the power of integrity. His masseur gave him the following verse just prior to his world record race. (1Samuel 2:30 "those who honor Me I will honor") As God's providence would have it a runner dropped out of the 400-meter race, scheduled on a weekday. Eric offered to fill the slot, even though this was four times as long as the race for which he had trained. When the 400 meters had concluded, not only did Eric win running away, but he did so in record time!  What Eric did was was "acceptable to God and approved by men" (Ro 14:18). And God did honor him. And men did approve of him. However Instead of basking in the glory & potential fortune that might have been his as an Olympic gold medalist, he chose to finish his education at the U. of Edinburgh. Upon graduation he left Scotland for the missionary fields of China. As he left the train station in Edinburgh, all the faculty, students & town sang "All Hail the Power of Jesus' Name" In China he was  captured by the Japanese during WWII & imprisoned with 1800 others in an area no bigger than 100 x 200 yards. In this difficult environment this man of integrity, proved to be a daily source of a righteous life lived out, bringing peace & joy, preaching, singing & ministering to his fellow prisoners, many of whom were also missionaries. He died there in 1945, shortly after his 43rd birthday, and just prior to the liberation. Although most of his fellow prisoners did not know it, Eric had been suffering headaches from what proved to be a brain tumor that caused his death. And yet despite his personal torment, this godly saint persevered to the end, proving to be a source of comfort, continuing to manifest his radiant smile literally up to the very day before he died. His biographer, Sally Magnusen, freely admitted the source of his spirituality: "He seemed to get his strength and self-discipline and his air of quiet serenity from his early-morning sessions of prayer, meditation, and Bible study. . . . somewhere in this daily discipline of faith lay the secret of the man, perhaps the secret of how he ran."

Eric Liddell presented a compelling model for how we should live, calling himself & others to an honest life & to self-sacrifice:

"Let us put ourselves before ourselves & look at ourselves. The bravest moment of a person's life is the moment when he looks at himself objectively without wincing, without complaining, [However] self-examination that does not result in action is dangerous. What am I going to do about what I see? The action called for is surrender -- of ourselves to God."

ANOTHER REGARDS EVERY DAY ALIKE: os de krinei (3SPAI) pasan hemeran:

The strong brother was unaffected by days. They were all a gift from God to him. Nowhere in the NT are Christians ever told to keep the Sabbath or the Lord's Day (Sunday). And yet at the same time we recognize the principle of one day in seven, one day of rest after six days of work.

LET EACH MAN BE FULLY CONVINCED IN HIS OWN MIND: hekastos en to idio noi plerophoreistho (3SPPM): (14,23; 1 Corinthians 8:7,11) (Isaiah 40:29) (1 John 3:19-21)

Each person should have a personal conviction about this matter. Each Christian must follow the dictates of his own conscience in matters not specifically commanded or prohibited in Scripture. Since conscience is a God-given mechanism to warn, and responds to the highest standard of moral law in the mind (see notes on Romans 2:14-15), it is not sensible to train yourself to ignore it. Rather, respond to its compunctions and as you mature, by learning more, your mind will not alert it to those things which are not essential.
 
It should however be clear that such a principle applies only to matters that are morally neutral -- the externals but not the eternals. When it comes to fundamental eternal doctrines of the Christian faith, there is no room for individual opinions. But in the area where things are neither right nor wrong in themselves, and Scripture is silent, there is room for differing views. They should not be allowed to become tests of fellowship, which far too often is the case in practice. Paul then is saying in essence "I know you are sometimes going to choose differently from each other, but by all means be confident in what you choose. Be settled in your conviction & don't be flipping back and forth." There is a reverse truth implicit here also, which is: If the Lord convicts you that something is wrong in your life, you had better not do it, even if other Christians are doing it!      

Lord (2962) (kurios is found 10 times Romans 14 and 38x altogether in Romans) in classical Greek, was used of gods, and the inscriptions applied to different gods (Hermes, Zeus, etc.) or also of the head of the family, who is lord of wife and children. In the present context kurios describes the One Who has absolute ownership and uncontrolled power.

No Christian has the right to "play God" in another Christian’s life. We can pray, advise, and even admonish, but we cannot take the place of God. What is it that makes a dish of food "holy" or a day "holy"? It is the fact that we relate it to the Lord. The person who treats a special day as "holy" does so "unto the Lord." The person who treats every day as sacred, does so "unto the Lord."

The Christian who eats meat gives thanks to the Lord, and the Christian who abstains from meat abstains "unto the Lord." To be "fully persuaded—or assured—in his own mind" (Ro 14:5) means: Let every man see to it that he is really doing what he does for the Lord’s sake, and not merely on the basis of some prejudice or whim. Some standards and practices in our local churches are traditional but not necessarily scriptural. Some of us can remember when dedicated Christians opposed Christian radio "because Satan was the prince of the power of the air!" Some people even make Bible translations a test of orthodoxy. The church is divided and weakened because Christians will not allow Jesus Christ to be Lord." (Wiersbe)

G Campbell Morgan writes the following note on this verse...

HE WHO OBSERVES THE DAY, OBSERVES IT FOR THE LORD: o phronon (PAPMSN) ten hemeran kurio phronei (3SPAI): (Galatians 4:10)

"He who observes the day, observes it in honor of the Lord." (Amplified)

"Those who have a special day for worshiping the Lord are trying to honor him." (NLT)

Those who have a special day for worshiping the Lord are trying to honor him. Do everything you do for the honor of Christ and a heart full of thanksgiving to Him (see notes Colossians 3:23-24). Note Paul's repeated emphasis on "for the Lord" (4x in Ro 14:4-8) in this area of why one does or does not do a "non-essential". 

Paul gave us similar principle that should be our guide in this area of externals in (1 Cor 10:31)

"Whether, then, you eat or drink or whatever you do, do all to the glory of God."

Their is no difference in motivation between the two groups (strong & weak)  -- both conduct themselves in the way they are led to do by their conscience so that they might please their Master , the Lord Jesus.

AND HE WHO EATS, DOES SO FOR THE LORD FOR HE GIVES THANKS TO GOD: kai o esthion (PAPMSN) kurio esthiei (3SPAI) eucharistei (3SPAI) gar to theo: (Isaiah 58:5; Zechariah 7:5,6)

When people eat all kinds of foods, they honor the Lord as they eat, since they give thanks to God. The evidence that both the “weak” and the “strong” have right hearts is that they both give “thanks” to God. That is, both do what they do with the intention of serving the Lord.

In Exodus Moses instructed Israel regarding the feast of unleavened bread...

 'Now this day will be a memorial to you, and you shall celebrate it as a feast to the LORD; throughout your generations you are to celebrate it as a permanent ordinance. (Exodus 12:14)

And similarly in regard to the Passover that...

It is a night to be observed for the LORD for having brought them out from the land of Egypt; this night is for the LORD, to be observed by all the sons of Israel throughout their generations. (Exodus 12:42)

And in regard to the Sabbath...

And Moses said, "Eat it today, for today is a sabbath to the LORD; today you will not find it in the field. (Ex 16:25)

Ray Stedman comments that...

God sees both of these men and both of these viewpoints as honoring him. The one who thinks Sunday is a special day that ought to be kept different from all other days is doing so as unto the Lord, therefore honor that, respect that viewpoint. The one who says, "No. When we are in Christ, days do not mean anything. They are not set aside for any special purpose. Therefore, I feel every day is alike, and I want to honor the Lord on every day." Okay, do not feel upset at that. He is doing so out of a deep conviction of his heart. The one who drinks beer gives thanks to God for the refreshment of it and the taste of it, and it is perfectly proper that he does so. The one who says, "No. I cannot drink beer. I only drink coffee," gives thanks for the coffee. The coffee may do as much physical harm as the beer, but, in either case, it is not a moral question. It is a question of what the heart is doing in the eyes of God. Sometimes we are too harsh with one another in these areas.

AND HE WHO EATS NOT, FOR THE LORD HE DOES NOT EAT, AND GIVES THANKS TO GOD:  kai o me esthion (PAPMSN) kurio ouk esthiei (3SPAI) kai eucharistei (3SPAI) to theo: (Matthew 14:19; 15:36; John 6:28; 1 Corinthians 10:30,31; 1 Timothy 4:3-5)

Vegetarians also honor the Lord when they eat, and they, too, give thanks to God. To count every moment absolutely devoted to God, and therefore holy in the highest sense, is the very essence of the new life in Christ

J Vernon McGee quips that...

"It is not what is on the table, but what is in the heart that is noted by God. It is the heart attitude that conditions Christian conduct." (Thru the Bible Commentary)

Paul’s indisputable point here is: people with opposing viewpoints on non-essentials can both be perfectly right with God. We need to take this to heart.

Two of the most famous Christians in the Victorian Era in England were Charles Spurgeon and Joseph Parker, both mighty preachers of the gospel. Early in their ministries they fellowshipped and even exchanged pulpits. Then they had a disagreement, and the reports got into the newspapers. Spurgeon accused Parker of being unspiritual because he attended the theater. Interestingly enough, Spurgeon smoked cigars, a practice many believers would condemn. In fact, on one occasion someone asked Spurgeon about his cigars, and he said he did not smoke to excess. When asked what he meant by excess, he waggishly answered,

“No more than two at a time.”

Who was right? Perhaps neither, perhaps both! Better yet would be to realize that the two could disagree and both be in the will of God. (see another anecdotal story about Spurgeon under the note for Ro14:22).