Adam Clarke on Deuteronomy 28:9

The Lord shall establish thee a holy people unto himself - This is the sum of all blessings, to be made holy, and be preserved in holiness.

If thou shalt keep, etc. - Here is the solemn condition; if they did not keep God's testimonies, taking them for the regulators of their lives, and according to their direction walking in his ways, under the influence and aids of his grace, then the curses, and not the blessings, must be their portion. See Deu 28:15, etc.