This is my favorite hymn and creed rolled into one. Sometimes I fall asleep reciting portions of it to myself. There's something about the rhythm, the call and response, as well as the laudatory content. The tradition has it thus: Ambrose began singing out a line of it at Augustine's baptism, Augustine, inspired by the Holy Spirit, called out the next line, and the two of them proceeded to cry out the entire Te Deum in tandem, the spiritual father and the newly baptized caught up in the inspiration of the Spirit, and voila, a great hymn was born. Luther considered it worthy of becoming a fourth creed.