John Chrysostom

Wonderful indeed were the things in the Temple, the Holy of Holies; and again awful were those things also that were done at Mount Sinai, "the fire, the darkness, the blackness, the tempest." For, it says, "God appeared in Sinai," and long ago were these things celebrated. The New Covenant, however, was not given with any of these things, but has been given in simple discourse by God. See then how he makes the comparison in these points also. And with good reason has he put them afterwards. …

Homily on Hebrews 32 ↗

Theophylact of Ohrid

He shows that if they do not endure and at the same time do not believe in the promises, they are far more guilty than those under the Old Testament. And see how he makes the comparison. Having shown the superiority of the New Testament over the Old in many respects, as is already known, he now sets forth also the great and wondrous events of the Old Testament that took place on Mount Sinai (Deut. 5:22), and shows that they are insignificant and cannot be compared with the events of the New Testament. …

Commentary on Hebrews ↗

Oecumenius

There is fire, for this reason, that God may appear more fearsome to those who were delivering the law. "And to darkness and gloom." Darkness and gloom signify the shadow of the Old Testament. For if those were figures, it is evident that until the truth came, the figures were obscure, while it was not known what they signified. Moreover, darkness also signifies the invisibility of God. "and to darkness," he says, "under his feet." (Ps. 17:10) "and a storm." By the word, storm, he excites them when they were sluggish. …

The Pseudo-Oecumenian Catena on Hebrews ↗

Thomas Aquinas

696. – Having warned them to avoid the evils of guilt, the Apostle now assigns the reason, which is based on a comparison between the Old and New Testaments. In regard to this he does two things: first, he makes the comparison; secondly, he argues from it (v. 25). In regard to the first he does two things: first, he mentions what pertains to the Old Testament; secondly, what pertains to the New (v. 22). …

Commentary on Hebrews ↗