Now the God of patience and comfort (the same word as before, though here in the Authorized Version rendered consolation) grant you to be like-minded (see on Romans 12:16), one with another according to Christ Jesus: that ye may with one accord with one mouth glorify the God and Father of our Lord Jesus Christ (so certainly, rather than, as in the Authorized Version, "God, even the Father of," etc.). Wherefore receive ye one another (cf. Romans 14:1, and note), even as Christ also received us (or you, which is better supported, and, for a reason to be given below, more likely) to the glory of God. As in Romans 15:3, the example of Christ is again adduced. The connection of thought becomes plain if we take the admonition, "Receive ye one another," to be mainly addressed to "the strong," and these to consist principally of Gentile believers, the "weak brethren" being (as above supposed) prejudiced Jewish Christians. To the former the apostle says, "Receive to yourselves with full sympathy those Jewish weak ones, even as Christ, though sent primarily to fulfil the ancient promises to the house of Israel only (see Romans 15:8), embraced you Gentiles ( ὑμᾶς) also within the arms of mercy" Thus the sequence of thought in Romans 15:8, seq., appears. "Unto the glory of God" means "so as to redound to his glory." Christ's receiving the Gentiles was unto his glory; and it is implied that the mutual receiving of each other by believers would be so too. The idea of God's glory being the end of all runs through the whole passage (cf. Romans 15:6, Romans 15:9, Romans 15:11).
For (the reading γὰρ is much better supported than δὲ. The essential meaning, however, of λέγω γὰρ is the same as of λέγω δὲ) I say (i.e. what I mean to say is this; cf. 1 Corinthians 1:12; Galatians 4:1: Galatians 5:16) that Jesus Christ was (rather, has been made, γεγενῆσθαι being the more probable reading than γενέσθαι) a minister of the circumcision (i.e. of the Jews) for the truth of God, to confirm the promises made unto the fathers (literally, the promises of the fathers): and that the Gentiles might glorify God for his mercy. Observe the expressions, ὑπὲρ ἀληθείας θεοῦ, etc., and ὑπὲρ ἐλέους, with reference respectively to the Jews and Gentiles. Christ's primary ministry was to "the house of Israel" (cf. Matthew 15:24), in vindication of God's truth, or faithfulness to his promises made through the patriarchs to the chosen race: his taking in of the Gentiles was an extension of the Divine mercy, to his greater glory. The infinitive δοξάσαι, in Romans 15:9, seems best taken in the same construction with βεβαιῶσαι in Romans 15:8, both being dependent on εἰς τὸ. As it is written, For this cause I will confess to thee among the Gentiles, and sing unto thy Name. This quotation from Psalms 18:49 or 2 Samuel 22:50, with those that follow, are for scriptural confirmation of God's purpose, which has just been spoken of, to include the Gentiles in his covenanted mercies to Israel, so that they too might glorify him. St. Paul, after a manner usual with him; follows cut a thought suggested in the course of his argument, so as to interrupt the latter for a while, but to return to it in 2 Samuel 22:13. All, in fact, from the beginning of 2 Samuel 22:8 to the end of 2 Samuel 22:12, is parenthetical, suggested by "even as Christ received you,." at the end of 2 Samuel 22:7. All this, it may be observed, is confirmatory of Pauline authorship. The first quotation introduces David, the theocratic king, confessing and praising God, not apart from the Gentiles, but among them. The second, from Deuteronomy 32:43, calls on the Gentiles themselves to join in Israel's rejoicing; the third, from Psalms 117:1, does the same; the last, from Isaiah 11:10, foretells definitely the reign of the Messiah over Gentiles as well as Jews, and the hope also of the Gentiles in him.