A. 12 For our rejoicing is this, the testimony of our conscience, that in simplicity and godly sincerity, not with fleshly wisdom, but by the grace of God, we have had our conversation in the world, and more abundantly to you-ward.
B. 13 For we write none other things unto you, than what ye read or acknowledge;
C. and I trust ye shall acknowledge even to the end;
B’. 14 As also ye have acknowledged us in part,
A’. that we are your rejoicing, even as ye also are ours in the day of the Lord Jesus.
2A. 15 And in this confidence I was minded to come unto you before, that ye might have a second benefit; 16 And to pass by you into Macedonia, and to come again out of Macedonia unto you, and of you to be brought on my way toward Judaea.
2B. 17 When I therefore was thus minded, did I use lightness? or the things that I purpose, do I purpose according to the flesh, that with me there should be yea yea, and nay nay?
2C. 18 But as God is true, our word toward you was not yea and nay.
2D. 19 For the Son of God, Jesus Christ, who was preached among you by us, even by me and Silvanus and Timotheus, was not yea and nay, but in him was yea.
2C’. 20 For all the promises of God in him are yea, and in him Amen, unto the glory of God by us.
2B’. 21 Now he which stablisheth us with you in Christ, and hath anointed us, is God; 22 Who hath also sealed us, and given the earnest of the Spirit in our hearts.
2A’. i. 23 Moreover I call God for a record upon my soul, that to spare you I came not as yet unto Corinth.
ii. 24 Not for that we have dominion over your faith,
iii. 24 but are helpers of your joy:
ii’. for by faith ye stand.
i’. 2:1 But I determined this with myself, that I would not come again to you in heaviness. 2 For if I make you sorry, who is he then that maketh me glad, but the same which is made sorry by me?
vs 21
A 21 Now he which stablisheth us with you in Christ,
B and hath anointed us,
C is God;
B’ 22 Who hath also sealed us,
A’ and given the earnest of the Spirit in our hearts.
That definitely looks like a chiasm to me and is not the first I’ve seen which appears to also be a part of another chiasm
Please consider from NASB95
A 21 Now He who ESTABLISHES US with you in Christ
B and ANOINTED US is God,
C 22 who also SEALED US
D and GAVE [US] THE SPIRIT IN OUR HEARTS AS A PLEDGE.
E 23 But I CALL GOD AS WITNESS TO MY SOUL,
E’ THAT TO SPARE YOU I DID NOT COME AGAIN TO CORINTH.
D’ 24 Not that we lord it over YOUR FAITH,
C’ but ARE WORKERS with you for your joy;
B’ for in YOUR FAITH
A’ you are STANDING FIRM.