Albert Barnes Commentary 2 Samuel 14:12

"Then the woman said, Let thy handmaid, I pray thee, speak a word unto my lord the king. And he said, Say on." — 2 Samuel 14:12 (ASV)

Having at last obtained what she wanted—the king’s oath that her son would not die—she proceeds to the case of Absalom. The meaning of 2 Samuel 14:13 can be paraphrased as follows: “If you have done right regarding my son, how can you hold such a vengeful purpose against Absalom, keeping him, one of God’s people, as an outcast in a pagan country, far from the worship of the God of Israel? By your own judgment, you are guilty of a great fault in not allowing Absalom to return.”

The king doth speak... - This literally means, “By the king speaking this word (this sentence of absolution for my son), he is as one who is guilty.” That is, the sentence you have pronounced in favor of my son condemns your own conduct toward Absalom.