18 But as God is faithful, our word to you was not Yes and No.
Paul answers the second question of verse 17 in verse 18.
18 But as God is faithful [true],
To justify his reason for not coming to Corinth when he said he would, Paul calls upon God to witness for him. Whatever God promises is true. He is always faithful to His Word. He forever means what He says (1 Co 1:9). This is the logic of non-contradiction. Two contradictory assertions cannot both be true with the same meaning and at the same time. Paul makes an oath before God by the phrase “as God is faithful,” or true. His message was consistent.
our word to you
The “word” here is the message or doctrine that Paul’s team preached. As God is faithful and true, so Paul’s team’s preaching was true.
was not Yes and No.
Paul does not say one thing then means another to the Corinthians. “Yes” and “no” are contradictory messages. HIs message that is inconsistent with itself. If the Corinthians put their trust in God’s faithfulness, then they should trust those who preach His Word that idea.
The stability of God’s promises is the basis for our actions.
God’s Word is faithful to us. His Word is unequivocal and does not fluctuate with a change in culture. He also stands behind those who proclaim His Word (2 Co 3:4-6).
If a Christian leader changes his plans arbitrarily, then people will lose confidence in him. This is especially true if his character demonstrates instability. If followers attribute fickleness to his integrity, then they may assign biblical doctrine to relativism or subject to change according to the dictates of culture.
There are popular preachers out there who are shifty opportunists. These people play with the souls of those who listen. Genuine preachers say what they mean and mean what they say. We often find the quality of character in the person who is consistent in his preaching.