Ambrose of Milan — as excerpted in the Catena Aurea on Luke 19:37-40

“Nor is it wonderful that the stones against their nature should chaunt forth the praises of the Lord, whom His murderers, harder than the rocks, proclaim aloud, that is, the multitude, in a little while about to crucify their God, denying Him in their hearts, whom with their mouths they confess. Or perhaps it is said, because, when the Jews were struck silent after the Lord’s Passion, the living stones, as Peter calls them, (1 Pet. 2:5.) were about to cry out.”