John Gill Commentary Deuteronomy 9:1

"Hear, O Israel: thou art to pass over the Jordan this day, to go in to dispossess nations greater and mightier than thyself, cities great and fortified up to heaven," — Deuteronomy 9:1 (ASV)

Hear, O Israel
A pause being made after the delivery of the preceding discourse; or perhaps what follows might be delivered at another time, at some little distance; and which being of moment and importance to the glory of God, and that Israel might have a true notion of their duty, they are called upon to listen with attention to what was now about to be said:

you are to pass over Jordan this day ;
not precisely that very day, but in a short time after this; for it was on the first day of the eleventh month that Moses began the repetition of the laws he was now going on with, (Deuteronomy 1:3) , and it was not until the tenth day of the first month of the next year that the people passed over Jordan, (Joshua 4:19) which was about two months after this:

to go in and possess nations greater and mightier than yourself ;
the seven nations named (Deuteronomy 7:1) where the same characters are given of them:

cities great and fenced up to heaven ;
as they were said to be by the spies, (Deuteronomy 1:28) , and were no doubt both large and strongly fortified, and not to be easily taken by the Israelites, had not the Lord been with them, (Deuteronomy 9:3) .