"For no matter how many promises God has made, they are 'Yes' in Christ" (vs. 20).
Because Paul apparently did not visit Corinth as he had planned (vs. 15), he is writing them a letter. The Corinthian Church is dear to Paul, and he wants them to be sure that he has not forgotten them.
As Paul begins to write to them, he includes a message about the comfort of God (vs. 3-7) and the trials of the apostles (vs. 8-11). He also pens an intriguing statement about the forthrightness of God, that He is decidedly not a God of both "Yes" and "No", with a sort of a wishy-washy changeable mind. Rather, God is determined to always follow up His statements and promises with a firm "Yes!" as revealed in Jesus Christ.
Christ is God's "Yes" to us!