Deuteronomy 6:13 (ESV) … “It is the Lord your God you shall fear. Him you shall serve and by his name you shall swear.”
The fear of the Lord—that reverent awe which is akin to love—is the beginning of wisdom and the foundation of piety; where it is in the heart it will lead to serving of the Lord in holy obedience; and they in whom it dwells will swear by his Name, recognizing his presence and omniscience, and not daring to asseverate anything but what they know to be true. Thus, really believing in God and reverently worshipping him, the Israelites would be careful not to go after other gods, or to give to any object that homage which is due unto Jehovah alone, knowing that this he will not endure or suffer with impunity; for he is a jealous God, and them that thus dishonour him he will destroy (Exod. 20:5; ch. 4:24, etc.).
Thus also they should be kept from murmuring against God, and thereby tempting him—putting him, as it were, to the proof, and calling in question his presence and his power, as they had done at Massah (Exod. 17:1–7). Without this genuine religious principle there will be no sincere worship, no true reverence, no real obedience, rendered unto God. But where this dwells in the heart it will influence the whole life, so that the commandments of God shall be diligently kept, and that which is good and right in his sight shall be done.