Ex 20:5

20:5 jealous. When used of God, this word describes His passion for His holy name, a zeal that demands the exclusive devotion of His people. It is employed when that claim is threatened by other deities (Deut. 6:15; Josh. 24:19).

third and the fourth generation. The longest span of generations represented in a given household at any one time. The severity of God’s judgment on subsequent generations warns those who love their children’s children of the terrible consequences of their sin.