Note: this attempt to discern the structure has a very large asymmetry in passage length. I think that verse 9 “God is faithful” is a comment on the fulfilled promise that the Corinthians would receive Spirit gifts and bring them to the Kingdom. As always, comments very much appreciated.
A. (1) Paul, called to be an apostle of Jesus Christ through the will of God, and Sosthenes our brother, (2) Unto the church of God which is at Corinth, to them that are sanctified in Christ Jesus, called to be saints, with all that in every place call upon the name of Jesus Christ our Lord, both theirs and ours: (3) Grace be unto you, and peace, from God our Father, and from the Lord Jesus Christ.
B.(4) I thank my God always on your behalf, for the grace of God which is given you by Jesus Christ; (5) That in every thing ye are enriched by him, in all utterance, and in all knowledge; (6) Even as the testimony of Christ was confirmed in you: (7) So that ye come behind in no gift; waiting for the coming of our Lord Jesus Christ: (8) Who shall also confirm you unto the end, that ye may be blameless in the day of our Lord Jesus Christ.
B’.(9) God is faithful,
A’. by whom ye were called unto the fellowship of his Son Jesus Christ our Lord.
2A.(10) Now I beseech you, brethren, by the name of our Lord Jesus Christ, that ye all speak the same thing,
2B. and that there be no divisions among you;
2C. but that ye be perfectly joined together in the same mind and in the same judgment.
2B’.(11) For it hath been declared unto me of you, my brethren, by them which are of the house of Chloe, that there are contentions among you.
2A’.(12) Now this I say, that every one of you saith, I am of Paul; and I of Apollos; and I of Cephas; and I of Christ.
3A.(13) Is Christ divided? was Paul crucified for you? or were ye baptized in the name of Paul?
3B.(14) I thank God that I baptized none of you, but Crispus and Gaius;
3C.(15) Lest any should say that I had baptized in mine own name.
3B’.(16) And I baptized also the household of Stephanas: besides, I know not whether I baptized any other.
3A’.(17) For Christ sent me not to baptize, but to preach the gospel: not with wisdom of words, lest the cross of Christ should be made of none effect.