All the commandments which I command thee this day shall ye observe to do, that ye may live, and multiply, and go in and possess the land which the LORD sware unto your fathers.
All the commandments ... shall ye observe ... that ye may live. Duty has been made in all the wise arrangements of our Creator inseparably connected with happiness; and the earnest enforcement of the divine law which Moses was making to the Israelites was in order to secure their being a happy, by being a moral and religious, people: a course of prosperity is often called life (Genesis 17:18; Proverbs 3:2).
And multiply. This reference to the future increase of their population proves that they were too few to occupy the land fully at first.