Bede

Jesus made his way to the Mount of Olives to announce that the peak of mercy consists in himself. He came again at daybreak to the temple to signify that, as the radiance of the New Testament was beginning, that same mercy was to be disclosed and presented to the temple, namely, to his faithful ones.…The Lord's sitting suggests the humility of his incarnation through which he deigned to show mercy to us.… It is good that we are told that when Jesus taught sitting down, all the people came to him. …

Homilies on the Gospels 1.25 ↗

Thomas Aquinas

Christ's return to the temple is described as being early; thus he says, and early in the morning he came again to the temple. This signifies that he was about to impart knowledge and manifest his grace in his temple, that is, in his believers: "We have received your mercy, O God, in the middle of your temple" (Ps 47:10). The fact that he returned early in the morning signifies the rising light of new grace: "His going forth is as sure as the dawn" (Hos 6:3). …

Commentary on John ↗

Bonaventure

"And at dawn he came again to the temple." Diligence is noted in this, that he came at dawn; Wisdom six: "She anticipates those who desire her, so that she may show herself to them first," and Proverbs eight: "Those who watch for me in the morning shall find me." It was also public: whence he says: "And all the people came to him": Luke twenty-one: "All the people came early in the morning," that is, went in the morning, "to him in the temple to hear him." It was also authoritative: therefore he says: "And sitting down he taught …

Commentary on John, Chapter 8 ↗