Augustine of Hippo

So, then, in some points that bear on the doctrine of salvation, which we are not yet able to grasp by reason—but we shall be able to sometime—let faith precede reason, and let the heart be cleansed by faith so as to receive and bear the great light of reason; this is indeed reasonable. Therefore the prophet said with reason: "If you will not believe, you will not understand"; thereby he undoubtedly made a distinction between these two things and advised us to believe first so as to be able to understand whatever we believe. …

Letter 120 ↗

Jerome

And Ahaz said, I will not ask, neither will I tempt the Lord. This is not humility, but pride, that he does not want to ask for a sign from the Lord. Although it is written in Deuteronomy: You shall not test the Lord your God (Deut. 6:16), and the Savior used this against the devil as a testimony (Matt. 4): nevertheless, being commanded to ask, he should have fulfilled the command in obedience, especially since both Gideon and Manoah asked for and received a sign (Judges 6 and 13). …

Commentary on Isaiah ↗

Thomas Aquinas

And the head of Ephraim, as above. If you will not believe. Here he places the condemnation of the unbelieving. If you will not believe, namely in the promises of the Lord, you too shall not continue in your land, but you will be taken captive: behold, he that is unbelieving, his soul shall not be right in himself (Hab 2:4). …

Commentary on Isaiah ↗