7 “Turn our captivity, O Lord, as the torrents in the south”. Consider, my brethren, what this means....As torrents are turned in the south, so turn our captivity. In a certain passage Scripture says, in admonishing us concerning good works, “Your sins also shall melt away, even as the ice in fair warm weather.” Our sins therefore bound us. How? As the cold binds the water that it run not. Bound with the frost of our sins, we have frozen. But the south wind is a warm wind: when the south wind blows, the ice melts, and the torrents are filled. Now winter streams are called torrents; for filled with sudden rains they run with great force. We had therefore become frozen in captivity; our sins bound us: the south wind the Holy Spirit has blown: our sins are forgiven us, we are released from the frost of iniquity; as the ice in fair weather, our sins are melted. Let us run unto our country, as the torrents in the south....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)