St. Ambrose: HEXAMERON 5.88: Commentary on Aeterne rerum conditor

A.S. Walpole, Early Latin Hymns, says that this section of the Hexameron is a commentary on St. Ambrose’s hymn, Aeterne Rerum Conditor: ‘the passage appears to be based on the hymn, rather than the hymn on the passage’.

St. Ambrose: HEXAMERON 5.88: Commentary on Aeterne rerum conditor

The cock's crow is pleasant at nightfall. It is not only pleasant, but useful, too. As a good domesticated fowl he arouses the sleeper, gives him warning when he is perturbed, and consoles the voyager by asserting in musical tones that night is approaching. When the cock crows, the thief forsakes his schemes and the star of dawn rises to illumine the sky. When the cock crows, the sailor's gloom and trepidation disappear. Tempests and storms stirred up by gusts of wind at evening tide subside. At his crowing the devout of heart bestir themselves for prayer and resume their reading. Finally, on this occasion 'the rock of the Church' washed away his sin which he had committed before the cock crowed. At cock-crow hope returns to all, the sick find comfort, the wounded find relief, the feverish are calmed, the lapsed return to the faith. Jesus has regard for those who stumble and corrects the errant. Hence He paid heed to Peter and forthwith the sin departed. Peter revoked his denial and his confession was completed. That this was God's plan and not a mere accident is revealed in the words of the Lord. It is written that Jesus said to Simon: 'Before the cock crows, thou wilt deny me three times.'

My translation of the hymn for comparison:

Eternal Creator of things, you who rule night and day, and give the time of the seasons that you may relieve our boredom. The cock, the watchman through the deep of night, now sounds, a nocturnal light for travelers, separating one night from another. By this the morning star is aroused, the sky is parted from the darkness; by this every band of errors abandons its harmful ways. By this the sailor regains his strength and the raging sea is calmed; by this Peter himself, the rock of the Church, by song washes away his guilt. O Jesus, look upon those who are falling, for by one glance you correct; if you see us, our lapses fall and crime is absolved by tears. You, O Light, shine on our senses, may sleep of our souls depart; our voices sing to you and our promises to you are kept.