WLC Q.133: What is the reason annexed to the fifth commandment, the more to enforce it?
The reason annexed to the fifth commandment, in these words, That thy days may be long upon the land which the Lord thy God giveth thee, (Exod. 20:12) is an express 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. (Deut. 5:16, 1 Kings 8:25, Eph. 6:2–3)