Was Jesus Christ, as preached by Paul, Silvanus, and Timothy, yea and nay or fickle?
The Christ preached by Paul, Silvanus, and Timothy was not yea and nay, nor fickle. The message about the Son of God was not superficial or frivolous; it was sure and full of meaning. In Him all God's promises are yea and amen, established and sealed by God.
Les explains that Paul was answering the charge that he had been frivolous or fickle about his plans and message. He did not speak in fickle language merely to tickle ears; whatever the apostle said, he meant fully, even though other things intervened. In verse 18, as God is true, their word toward the Corinthians was not yea and nay. The Son of God, Jesus Christ, preached among them by Paul, Silvanus, and Timothy, was not yea and nay, not fickle or superfluous. Instead, all the promises of God in Him are yea and amen. Les also notes God establishes, anoints, seals, and gives the earnest, or down payment, of the Spirit in believers' hearts, with Ephesians 1 as a parallel about their position in the Body of Christ.
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.