John Gill Commentary Deuteronomy 11:8

"Therefore shall ye keep all the commandment which I command thee this day, that ye may be strong, and go in and possess the land, whither ye go over to possess it;" — Deuteronomy 11:8 (ASV)

Therefore shall you keep all the commandments which I command
you this day
For the reasons before suggested, as well as for what follow:

that you may be strong ;
healthful in body, and courageous in mind, for sin tends to weaken both; whereas observance of the commands of God contributes to the health and strength of the body, and the rigour of the mind; both which were necessary to the present expedition they were going upon:

and go in and possess the land where you go to possess it ;
the land of Canaan, they were marching towards in order to possess it; and nothing would more inspire them with courage, and cause them to enter it manfully without fear of their enemies, than obedience to the commands of God; whose presence being promised them on that account, they might expect it, and so had nothing to fear from the inhabitants of the land.