And Moses came - Probably from the tabernacle, where God had given him this prophetic ode, and he rehearsed it in the ears of the people.
Albert Barnes
Notes on the Whole Bible
Verses 44-52
These verses were, no doubt, added by the author of the supplement to Deuteronomy. For the statements contained in them, consult the marginal references.
Matthew Henry
Concise Bible Commentary
Here is the solemn delivery of this song to Israel, with a charge to mind all the good words Moses had said unto them. It is not a trifle, but a matter of life and death: mind it, and you are made for ever; neglect it, and you are for ever undone. Oh that men were fully persuaded that religion is their life, even the life of their souls!