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.  And thou shalt remember all the way which the LORD thy God led thee these forty years in the wilderness, to humble thee, and to prove thee, to know what was in thine heart, whether thou wouldest keep His commandments, or no.  And He humbled thee, and suffered thee to hunger, and fed thee with manna, which thou knewest not, neither did thy fathers know; that He might make thee know that man doth not live by bread only, but by every word that proceedeth out of the mouth of the LORD doth man live.
Deuteronomy 8:1-3

On these two commandments hang all the Law and the Prophets.
Matthew 22:40

And he said, “The God of our fathers hath chosen thee, that thou shouldest know His will, and see that Just One, and shouldest hear the voice of His mouth.  For thou shalt be His witness unto all men of what thou hast seen and heard…”
Acts 22:14-15