Isaiah 7:12

Ahaz refused to ask for a sign. He did not want God to confirm that He would protect Judah because he had already decided not to trust God but to make other arrangements. He tried to justify his disobedience and his lack of faith with a pious statement that he did not want to test Yahweh (cf. Deuteronomy 6:16). Testing the Lord got Israel into big trouble in the wilderness and at other times, but asking for a sign was not testing God when He commanded it. God prohibited testing Him (demanding proof) when His people doubted or rebelled against Him (cf. Psalms 95:9; Matthew 16:4; Mark 8:12; Luke 11:29), not when they wanted a sign to strengthen their faith (cf. Judges 6:36-40; 2 Kings 20:8-11; Psalms 34:6; Malachi 3:10). Ahaz wanted to appear to have great faith in God, but he had already decided to make an alliance with Assyria.

"This was like a mouse sending for the cat to help him against two rats!" [Note: Alfred Martin, Isaiah: "The Salvation of Jehovah," p. 39.]

Ahaz may even have convinced himself that this alliance was the means God would use to deliver Judah. A sign from God would only prove that Ahaz’s plan was contrary to God’s will. Compare King Saul’s refusal to obey God and its consequences.