Charles Ellicott Commentary Deuteronomy 6:3

"Hear therefore, O Israel, and observe to do it; that it may be well with thee, and that ye may increase mightily, as Jehovah, the God of thy fathers, hath promised unto thee, in a land flowing with milk and honey." — Deuteronomy 6:3 (ASV)

That you may increase mightily ... in the land. —The position of Israel in the land, and their continuance in it, depended entirely on their fulfillment of the purpose for which they were brought there—the observance of the Law of Jehovah, as it applied to their specific situation.