Quoting from the fifth commandment, Paul shows how his instruction agrees with the eternal moral law. First of all it teaches all people to honour their parents.
Paul calls this ‘the first commandment with promise.’ He says this to encourage us to obey it, by pointing to the blessing that comes from the Lord in keeping it. There should be deep love between parents and their children, and there is new wisdom to be passed from parents to children even in the last stage of life. The communication is two-way and parents also learn about and take a deep interest in the lives of their children.
Some see the statement that this is ‘the first commandment with promise’ as a problem, since they note what they believe to be an earlier promise attached to the second commandment: ‘For I the LORD thy God am a jealous God, visiting the iniquity of the fathers upon the children unto the third and fourth generation of them that hate me; and shewing mercy unto thousands of them that love me, and keep my commandments.’ This is explained in various ways. It is said that Paul does not mean that the fifth commandment is the first in order of the ten, but that it is the first in order of importance. This however weakens his statement and puts the commandments in an order of importance which the Scripture does not assign to them. Another solution is to see that the statement attached to the second commandment is not a promise, but is a description of the character of God. His name is not to be taken in vain because he is such a God. Further evidence that it is not a bare promise comes from noting that it carries a negative as well as a positive statement about God, and the negative comes first. Nor is it worded like the promise attached to the fifth, in which man is told do something and then a promise is added for his encouragement. Furthermore, the fifth commandment is positive, ‘Honour …’, while the second commandment is a prohibition, ‘You shall not make … you shall not bow down …’, to which no promise can be attached directly, but only a threat. The merciful side of God’s character comes after the warning and is addressed to those who out of respect for God’s name would do the opposite of what is forbidden in the commandment. Of course everything about the character of God can be expected to have an encouraging effect on our behaviour, but according to this explanation, Paul is entirely correct in calling this the first commandment with promise.