Charles Spurgeon Commentary Deuteronomy 29:1

"These are the words of the covenant which Jehovah commanded Moses to make with the children of Israel in the land of Moab, besides the covenant which he made with them in Horeb." — Deuteronomy 29:1 (ASV)

That is the preamble, just as in legal documents there is usually some statement of the purpose and intent of the legal contract before proceeding with the main content. These covenants with God are solemn things, and therefore they are given in a formal manner to capture attention and demand our serious consideration.