Theophylact of Ohrid

After this He teaches them that "thus it was necessary for Christ to suffer." How then is it "thus"? On the wood of the Cross. Since destruction entered through a tree, corruption also had to be destroyed through a tree, and the delight of the tree had to be abolished by the Lord, who unconquerably endured the sufferings on the tree.

Commentary on Luke ↗

Bede

The disciples learned that their Maker subjected himself to countless kinds of abuses at the hands of the wicked and even to the sentence of death for their salvation. This effectively stirred them up to tolerate adversities of every kind for their salvation. They remembered that through his sacraments they had been cleansed, sanctified and united to the body of him who, when he had tasted death for them, presented an example of a speedy rising from death. …

Homilies on the Gospels 11.9 ↗

Bonaventure

Now these mysteries of the Scriptures are principally referred to Christ with regard to the head and with regard to the body. With regard to the head, he adds: And he said to them: Thus it is written, and thus it was necessary for Christ to suffer and to rise from the dead on the third day: this is most frequently stated in the Scriptures, and especially in the Law through figures, in the Prophets through words, and in the Psalms most abundantly, because they treat of the resurrection and the passion. …

Commentary on Luke, Chapter 24 ↗