John Chrysostom

"By faith" (he says) "Noah being warned of God." As the Son of God, speaking of His own coming, said, "In the days of Noah they married and were given in marriage," therefore the Apostle also recalled to their mind an appropriate image. For the example of Enoch, was an example only of Faith; that of Noah, on the other hand, of unbelief also. And this is a complete consolation and exhortation, when not only believers are found approved, but also unbelievers suffer the opposite. For what does he say? …

Homily on Hebrews 23 ↗

Theophylact of Ohrid

Noah, he says, "received a revelation" from God, that is, was instructed concerning unknown matters and did not remain unbelieving. On the contrary, though the air was clear, everyone was given over to indulgence and expected no danger, for nothing of the sort was noticeable, yet he, having believed God, feared the flood and prepared the ark, by means of which he saved all his household from the flood (Gen. 6:22). …

Commentary on Hebrews ↗

Oecumenius

"By faith, Noah, having been warned." Connect the "by faith" with "being cautious," so that it reads: "having been warned by faith, Noah prepared an ark concerning things not yet seen, being cautious and fearful." For it was by faith that he heard what would be the flood, to be cautious and terrified. "having been warned." Having heard from God. Elsewhere it is said, "He was warned by the Spirit." (Luke 2:26) Do you see equality? Just as the Father calls, so also does the Holy Spirit. "of things not yet seen." He speaks of the flood. …

The Pseudo-Oecumenian Catena on Hebrews ↗

Thomas Aquinas

578. – Then (v. 7) he shows what Noah did by faith and what he obtained as a result: and was instituted heir of the justice which is by faith. He mentions five things that he did: first, that he believed God's words about the judgment to come, but which was not yet seen. Hence, he says, By faith, Noah, being warned by God concerning events as yet unseen, believed. …

Commentary on Hebrews ↗