Q.71: What is the reason annexed to the fifth commandment?
A. The reason annexed to the fifth commandment is a promise of long life and prosperity (as far as it shall serve for God’s glory, and their own good) to all such as keep this commandment.
Honor your father and your mother, as the LORD your God has commanded you, that your days may be long, and that it may be well with you in the land which the LORD your God is giving you. Deuteronomy 5:16