Saint John Chrysostom:
In a spiritual sense, the coming of the New Testament is a new song: everything that happened then was new - testament (“I shall make a new testament with you," Scripture says), creation (“If anyone is in Christ,” Scripture says, "there is a new creation”), human being (“Having stripped off the former self,” Scripture says, “and put on the new, renewed in knowledge according to the image of the one creating it") On account of the new life, then, and everything else, it is called a New Testament, and the inspired author urge us now to sing a new song typical of it. In a historical sense, on the other hand, it is the famous and remarkable song they were due to sing for the victories, the doughty deeds, and the trophies.
Praise of him in the assembly of the holy ones. Do you see how he is looking for thanksgiving in life and action, and draws these people into the chorus of those singing praise? It is not sufficient, you see, to give thanks in word only if virtue in action does not accompany it. Praise of him in the assembly of the holy ones. He teaches us something else here: he shows that we must offer praise together and in complete harmony, assembly being a word meaning composition and gathering.