Theophylact of Ohrid

When the Lord had calmed and quieted the hearts of the disciples, having assured them of the reality of the resurrection of His body through His words, by allowing them to touch Him, and by partaking of food, then He opened their mind to understand the Scriptures. For if their soul had not been calmed, how would they have understood, being in a state of disorder, in a state of confusion? For "Be still," it is said, "and know" (Ps. 46:10).

Commentary on Luke ↗

Cyprian

Then opened He their understanding, that they might understand the Scriptures; and said unto them, That thus it is written, and thus it behoved Christ to suffer, and to rise again from the dead the third day; and that repentance and remission of sins should be preached in His name even among all nations."

Treatise XII Three Books of Testimonies Against the Jews ↗

Bede

Then he opened their minds to understand the Scriptures, and he said to them: Because it is written thus, and thus it was necessary for Christ to suffer, and to rise from the dead on the third day. He offers himself to be seen with the eyes, he offers himself to be handled by the hands. It is not enough to read, he recalls the Scriptures. And this is not enough, he opens the mind, so that what you read you understand. Then after commending the truth of his body, he commends the unity of the Church.

On the Gospel of Luke ↗

Bonaventure

Second, with regard to the infused light of understanding, he adds: Then he opened their understanding, that they might understand the Scriptures: he, I say, opened, because he alone holds the key, according to that passage in Isaiah twenty-two: "I will give him the key of David, and he shall open, and none shall shut; and he shall shut, and none shall open." And therefore the Prophet asks in the Psalm: "Open my eyes, and I will consider the wondrous things of your law"; because, in Daniel two, "he reveals deep things and knows what …

Commentary on Luke, Chapter 24 ↗