"Wherefore" (a term of conclusion) includes the entire section from (Ro14:1-15:6), and here sums up the major emphasis of this section. In immediate context because the purpose of being of one accord is to bring glory to God the Father, we are therefore to accept one another that this glorious effect might be realized.

Stedman asks the question...

"Do you remember the prayer of the little girl who once prayed, "Lord, make the bad people good and the good people nice"? This is really the subject of Ro14-15 -- making good people nice! One of the problems of the Christian church is that we may be quite correct in our doctrine and practice, but very irritating about it. How do you live with people like that? That is the problem of these chapters, and it is a problem that abounds everywhere -- how to live with other Christians who persist in looking at things differently than you do."

ACCEPT (14:1,v3) (a whole hearted attitude & action) ONE ANOTHER (Mt10:40 Mk9:37 Lu9:48): Dio proslambanesthe (2PPMM) allelous:

"Accepted" (proslambano) (4355) Paul commands us to make this our habit, our lifestyle. (For an interesting discussion of the "one another" commands in the NT click here.)

Proslambano is always in the MIDDLE VOICE in the NT which conveys the idea that the subject not only initiates the action but also participates in the results of that action.

So Paul says continually draw one another to yourself (that's the idea of the middle voice).

Give them a warm welcome.

Grant them access to your heart.

Take them to yourself.

Treat them as the closest of friends with the most caring kindness.

Believers are to receive one another in the closest of bonds. Let your love be without hypocrisy (Ro12:9) and demonstrate a genuine heartfelt acceptance. Take them into friendship. And remember that in the final analysis to accept one another is actually to accept Christ Himself (Mt10:40)

JUST AS CHRIST ALSO ACCEPTED US (14:3) TO THE GLORY OF GOD (Ro 5:2): kathos kai o Christos proselabeto (3SAMI) humas eis doxan tou theou:

It should not be too difficult to extend the hand of friendship to one who is loved by the One we honor and worship & Who first loved us.

The idea should be "Any friend of His is a friend of mine."

The same verb proslambano in (Ro14:3) describes God accepting the strong brother.

What were we like before Christ accepted us?

See (Ro 5:6-10) "helpless...ungodly...sinners...enemies".

So what excuse do we have not to accept another, no matter what the differences we might have with them in the arena of non-essentials. Jesus accepts sinners impartially (Ro 2:11).

Jesus accepts sinners to the glory of God. God established His eternal plan of redemption to glorify Himself. Everything He does is to His glory, and everything His children do should be to His glory.

Leenhardt writes

"Nothing glorifies God as much as the unity of His children, which alone is in harmony with His essential will of love."

Believers are to receive one another even as Christ has received us. No person is too prejudicial or critical, too weak or base for us to receive. The point is that Christ received and ministered to the most prejudicial and judgmental (the Jews), sinful and base (the Gentiles) people in the world; therefore, believers can receive one another (Gal3:28 Ep2:11-22). No one is too far gone to be rejected and cast away.

Ray Stedman has some practical insights writing:

"Now, that is the end and aim of human life, to "glorify the God and Father of our Lord Jesus Christ." Every Christian heart wants that. Is there any Christian who, deep down in his heart, does not want the glory of God in his life? Well, then, the way to produce it is to live in harmony with one another. That is the procedure. It says that even though Christians: Hold different points of view (they do not come to some universal agreement on doctrine -- that isn't what is necessary), despite this, they can be so interested in one another and so concerned about one another that they can live in harmony, and the result is that they glorify God. What is the key to it? It is tucked away in one little phrase which, if you miss it, you will want to live in harmony with others but you will find yourself quite incapable of doing it. The key is this little phrase, "in accord with Christ Jesus." (Ro15:5b) You see, when Paul mentions that Christ did not please Himself, he is not holding Him up as an example to follow, he is lifting Him up as a life to appropriate! That is the big difference! We are not just to try our best to live the same way, because we CAN'T. Our own natural inclinations of self-pleasing rise up and refuse to permit us to do that. But we must never forget that these exhortations that we read in these last five chapters of Romans rest solidly and squarely on the teachings of Ro5, 6, 7, 8. It is back there that we learn that God has done something about this old Adamic life which naturally moves to evil -- has cut it off, and has given us, in place of it, the indwelling life of the Son of God Himself, and it is His purpose and desire to live that life again through us! In the doing of it, we find it quite possible to do all that He does because He does it through us. This is what it is speaking of here when it says, "in accord with Christ Jesus," that is, in fellowship with him. Biting your lip, and trying to keep your temper is not the SECRET of living with difficult people; that is never it. The SECRET is a thankful heart which continually looks up to the Lord Jesus. It says, "Thank You, Lord, for the quietness and the calmness, the purity and the love which is available to me through You continually. Thank You." A thankful heart and an obedient will that seeks to please another for his own good is the SECRET of living with difficult people. You try that and see if it doesn't work."

John MacArthur adds that

"Paul does not mention specific types of believers in this verse. He is speaking to the strong and to the weak, to Gentiles and to Jews. All believers are called to accept one another. He is not simply speaking of accepting new believers into our church fellowship, although that would certainly be included in this admonition. He is calling on all Christians to accept one another in the fullest and deepest sense, to treat each other with love and understanding, just as Christ also accepted us. If the perfect, sinless Son of God has accepted us into God’s divine family, how much more should we be willing to accept each other, despite the fact that we all still carry sinful trappings from our old, unredeemed flesh."

Paul has explained that believers are to accept one another just as Christ accepted each one of us & now he elaborates on what Christ's acceptance of us entails -- in a nutshell, as menial (diakonos) (see in depth discussion of related word diakonia) servant, of both Jews and Gentiles.

Paul used perfect tense for "become" indicating a permanent state -- Christ continues in his capacity as "a servant of circumcision". His function as Jewish Messiah is permanent.

Paul is explaining the breadth of Christ's acceptance of us. Christ received the Jews and ministered to them & He did so for the truth of God -- to confirm and fulfill the promises God made to the patriarchs. Did He accept them because they accepted Him? In fact they did not receive Him! (Jn1:11) and yet Christ came to them & received & ministered to them. Why? For the sake of the truth of God—to fulfill the OT promises made in the Word of God for "not one word has failed of all His good promise" (1Ki8:56 cp Jos23:14 Nu23:19)

"Circumcision" is peritome (G4061) which in turn is from the verb peritémno [G4059] which means literally to cut around & then to circumcise.

The Jews took great pride in circumcision which became a badge of their spiritual and national superiority thus fostering a spirit of exclusivism instead of a missionary zeal to reach out to the Gentile nations as God had intended. A daily prayer of strict Jewish males was to thank God that he was neither a woman, a Samaritan, nor a Gentile. Gentiles came to be regarded by the Jews as the “uncircumcision,” a term of disrespect implying that non-Jewish peoples were outside the circle of God’s love. Paul had already dealt with genuine (internal, heart) circumcision and contrasted this with the external ritual (Ro2:28-29).

TO CONFIRM (make firm, strengthen, guarantee) THE PROMISES GIVEN TO THE FATHERS: eis to bebaiosai (AAN) tas epaggelias ton pateron:  (Ro9:4,5 )

How did Messiah confirm the promises to the patriarchs? Clearly by being the ultimate fulfillment of those OT promises (To Abraham Gen12:3 17:7 18:19 22:18 Ac3:25) (To Isaac Gen 26:3-4) (To Jacob Gen28:13-15 46:2-4).

Paul made it clear both that the covenant promises of God are permanent and that they find their fulfillment in Christ.

Paul's point is that herein lies our motivation to accept one another, to bear one another's weaknesses & not to please our self but build up one another (Ro15:1-2).

The believer has the greatest pattern imaginable:
Christ Himself.

The saved Jew primarily praises God for His truth & the saved Gentile primarily praises God for His mercy. Christ received the Gentiles and ministered to them. He came to bring them the mercy of God, that they might praise God for His mercy. And don't forget the context -- Jesus received & ministered to the Gentiles when they were living the most licentious & indulgent life-style imaginable (Ro1:18-32).

God had made covenants only with Israel (9:4), not with the Gentiles (Ep2:12), so God had no covenantal promises to confirm with the Gentiles. Any spiritual blessings that come to the Gentiles spring solely from the mercy of God. Nevertheless God eternally purposed to bless the Gentiles spiritually through the Lord Jesus as their Messiah and through His covenants with Israel (Ge 12:3 cf. Jn4:22).

It is no accident that Paul's quotations in (v8-12) are taken from the three divisions of the OT, the Law, the Prophets, & the Psalms (Lu24:44) & from three great Jewish heroes: Moses, David, and Isaiah.

A progression of thought can be traced through the four quotations. In the first, David praised God among the Gentiles (Ro15:9); in the second, Moses exhorted the Gentiles, Rejoice . . . with His people (Ro15:10); in the third the psalmist commanded the Gentiles to praise the Lord (Ro15:11; cf. v7) and in the fourth, Isaiah predicted that the Gentiles will live under the rule of the Root of Jesse (the Messiah) and they will hope in Him (Ro15:12).

AS IT IS WRITTEN THEREFORE I WILL GIVE PRAISE TO THEE AMONG THE GENTILES: kathos gegraptai (3SRPI) dia touto exomologesomai (1SFMI) soi en ethnesin:

To illustrate that it has always been God’s plan to bring Gentile into His kingdom, Paul cites the OT, possibly to soften the prejudice of Christian Jews against Christian Gentiles as their own Scriptures demonstrate that the inclusion of Gentiles was neither a divine nor a human afterthought.

This first OT quotation is from the Greek Septuagint of (2 Sa 22:50, Ps 18:49) where David is praising God for giving him victory over his enemies and for making the nations subject to him. David goes on to say will sing hymns of praise to the Lord among the Gentile nations, so that the Gentiles may know the true God and join in the praise.

Paul sees in this Psalm as a clear indication of God’s plan to include the Gentiles in the Messiah’s people. Israel was to have been the instrument through which God's redemptive work would extend to the Gentiles.

AND I WILL SING TO THY NAME: kai to onomati sou psalo (1SFAI):

"Sing" (psallo) (G5567) is derived from psáo which means to touch lightly, twang or snap.