A God of Yes

For the Son of God, Jesus Christ, who was preached among you by me and Silas and Timothy, was not "Yes" and "No," but in him it has always been "Yes."
2 Corinthians 1:19


Barnes' Notes on the Bible
For the Son of God - In this verse, and the following, Paul states that he felt himself bound to maintain the strictest veracity for two reasons; the one, that Jesus Christ always evinced the strictest veracity 2 Corinthians 1:19; the other, God was always true to all the promises that He made 2 Corinthians 1:20; and as he felt himself to be the servant of the Saviour and of God, he was bound by the most sacred obligations also to maintain a character irreproachable in regard to veracity on the meaning of the phrase "Son of God," see the note, Romans 1:4. Jesus Christ - It is agreed, says Bloomfield, by the best commentators, ancient and modern, that by Jesus Christ is here meant his doctrine. The sense is, that the preaching respecting Jesus Christ, did not represent him as fickle, and changeable; as unsettled, and as unfaithful; but as true, consistent, and faithful. As that had been the regular and constant representation of Paul and his fellow-laborers in regard to the Master whom they served, it was to be inferred that they felt themselves bound sacredly to observe the strictest constancy and veracity. By us ... - Silvanus, mentioned here, is the same person who in the Acts of the Apostles is called Silas. He was with Paul at Philippi, and was imprisoned there with him Acts 16, and was afterward with Paul and Timothy at Corinth when he first visited that city; Acts 18:5. Paul was so much attached to him, and had so much confidence in him, that he joined his name with his own in several of his epistles; 1 Thessalonians 1:1; 2 Thessalonians 1:1. Was not yea and nay - Our representation of him was not that he was fickle and changeable. But in him was yea - Was not one thing at one time, and another at another. He is the same, yesterday, today, and forever. All that he says is true; all the promises that he makes are firm; all his declarations are faithful. Paul may refer to the fact that the Lord Jesus when on earth was eminently characterized by truth. Nothing was more striking than his veracity. He called himself "the truth," as being eminently true in all his declarations. "I am the way, and the truth, and the life;" John 14:6; compare Revelation 3:7. And thus Revelation 3:14 he is called "the faithful and true witness." In all his life he was eminently distinguished for that. His declarations were simple truth; his narratives were simple, unvarnished, uncolored, unexaggerated statements of what actually occurred. He never disguised the truth; never prevaricated; never had any mental reservation; never deceived; never used any word, or threw in any circumstance, that was suited to lead the mind astray. He himself said that this was the great object which he had in view in coming into the world. "To this end was I born and for this cause came I into the world, that I should bear witness unto the truth;" John 18:37. As Jesus Christ was thus distinguished for simple truth, Paul felt that he was under sacred obligations to imitate him, and always to evince the same inviolable fidelity. The most deeply felt obligation on earth is that which the Christian feels to imitate the Redeemer.
 - Bible.cc