2 Corinthians 1:19

For the Son of God, Jesus Christ, who was preached among you by us, even by me and Silvanus and Timothy, was not yea and nay, but in him is yea.

By me and Sylvanus and Timothy ... These were with Paul in the founding of the church at Corinth; and the very fact of their having preached the truth that is in Christ Jesus made it morally impossible for them to have engaged in the kind of petty deceptions alleged against him by his foes.

In him is yea ... "Yea and nay" continues to be used here as an idiom of fraud and deception. In Christ there is neither fraud nor deception; but in him is yea; and in this context "yea" is an idiom for utmost truth, sincerity and integrity. This verse means that integrity is the hallmark of every Christian. Being "in Christ" is one and the same thing as being absolutely honest, truthful and straightforward in all communications of every kind. In the light of this, is it not true that some who may claim to be so are not really "in Christ" at all?

Sylvanus ... This is the same person identified as Silas in Acts 15:32,40, who was one of the prophets of the early church, and also a companion of Paul on the second missionary tour. He was with Paul in jail at Philippi and throughout that exciting tour.