Charles Ellicott Commentary Deuteronomy 32:47

"For it is no vain thing for you; because it is your life, and through this thing ye shall prolong your days in the land, whither ye go over the Jordan to possess it." — Deuteronomy 32:47 (ASV)

For it is not a vain thing for you. —Not too light a thing for you, not unworthy of your attention.

It is your life. —For the last time in this book, the people are assured that the very purpose of their existence in Canaan was the observance of the law of Jehovah as the law of the land.