Theophylact of Ohrid

He shows in what way Levi paid tithes, saying that since the forefather paid tithes, so too did he, by virtue of the fact that being already in the loins of Abraham, he was to be born from his seed, although he had not yet been born. And he did not say "the Levites," but Levi, in order to show the superiority. What boldness! He completely overturned everything Jewish. That is why he said before: "you have become dull of hearing" (Heb. …

Commentary on Hebrews ↗

Oecumenius

"For he was still in the loins." The seed that was the beginning of Levi's life was within the loins of Abraham. Indeed, Isaac was the cause and origin of Levi.

The Pseudo-Oecumenian Catena on Hebrews ↗

Thomas Aquinas

346. – Then (v. 10) he explains what he had said; and he says that Levi was still in the loins of his father, Abraham, when he gave tithes to Melchizedek, who met him. Consequently, when Abraham was tithed, Levi was tithed. But on the other hand: Christ, too, was in his loins, just as Levi: 'The son of David, the son of Abraham' (Mt. 1:1). Therefore, if the reason why Melchizedek is greater than Levi is that Levi was tithed, there seems to be no reason why Christ was not tithed; consequently, Melchizedek is still greater than Christ. …

Commentary on Hebrews ↗