John Chrysostom

"This is the stone," he says, "which was set at nought of you builders, which is become the head of the corner." He reminds them also of a saying which was enough to frighten them. For it had been said, "Whosoever shall fall on this stone shall be broken; but on whomsoever it shall fall, it will grind him to powder."

Homily on Acts 10 ↗

Theophylact of Ohrid

Such is — that is, thoroughly tested — that stone which became the head of these two peoples, united through it into one building of the Church: the believing Jewish people and all the believing Gentiles.

Commentary on Acts ↗

Oecumenius

And the phrase, "This is the stone," does not refer to the lame man, but to Jesus Christ, in whose name the lame man was healed. This stone, though rejected by you who were appointed for the building, has become for the house the chief cornerstone of faith, joining together both walls, the people from the Jews and those from the Gentiles, into agreement of one faith.

Commentary on Acts ↗

Bede

This is the stone which was rejected by you builders, which has become the chief cornerstone. The builders were the Jews, who, while all the nations were dwelling in the desolation of idols, they alone were reading the law and the prophets daily for edification. As they were building, they came upon the cornerstone, which would embrace two walls, that is, they found in the prophetic Scriptures that Christ would come in the flesh and build two peoples in Himself. …

Commentary on Acts ↗