Contradiction with Matthew 5:37
2 Corinthians 1:23 involves making an oath, while Matthew 5:37 advises against making oaths and encourages simple, honest communication.
Matthew 5:37: But let your communication be, Yea, yea; Nay, nay: for whatsoever is more than these cometh of evil.
Contradiction with James 5:12
Like Matthew 5:37, this verse urges believers not to swear oaths, contradicting Paul's calling God as a witness in his statement in 2 Corinthians 1:23.
James 5:12: But above all things, my brethren, swear not, neither by heaven, neither by the earth, neither by any other oath: but let your yea be yea; and [your] nay, nay; lest ye fall into condemnation.