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 mother,” which is the first commandment with promise: “that it may be well with you and you may live long on the earth.” Eph 6:2-3