John Chrysostom

"For to which of the Angels said He at any time, Thou art My Son, this day have I begotten Thee. And again, I will be to Him a Father, and He shall be to Me a Son"? For these things indeed are spoken with reference also to the flesh: "I will be to Him a Father, and He shall be to Me a Son" - while this, "Thou art My Son, this day have I begotten Thee," expresses nothing else than "from [the time] that God is." For as He is said to be, from the time present (for this befits Him more than any other), so also the [word] "To-day" seems …

Homily on Hebrews 2 ↗

Theophylact of Ohrid

From where, he says, is it evident that He is better than the angels? From His name: the name Son signifies true birth, that is, that He is from Him. If He is Son by grace, then He is lower than the angels. The expression "Today I have begotten You" means nothing other than that He is from the beginning, from which the Father also is. …

Commentary on Hebrews ↗

Oecumenius

We heard, and we who are men, are true sons through grace. The angels, however, did not hear this, lest their sublimity be thought to be from nature rather than from grace. Christ, however, is not from grace, but from nature. "I have begotten You." The Father relates the birth of the Son according to the flesh, therefore he said: "today"; Thus says the holy Athanasius.

The Pseudo-Oecumenian Catena on Hebrews ↗

Thomas Aquinas

48. – Then (v.5) he proves what he has said: first, he discusses the name inasmuch as it belongs to Christ according to His divinity; secondly, inasmuch as it belongs to Him according to His human nature (v. 5b). 49. – In regard to the first he adduces the authority of Ps. 2 (v.7): 'The Lord said to me: You are my son; this day have I begotten you.' And this in answer to the question: To what angel has God ever said, You are my son? As if to say: He never said these words to any of the angels, but to Christ alone. …

Commentary on Hebrews ↗