Ecclesiastes12:13 Let us hear the conclusion of the whole matter: Fear God, and keep his commandments: for this is the whole duty of man.
Solomon spend a good portion of his life seeking satisfaction apart from God. He tried wine, women, and song. He tried humor, building projects, and riches. He tried everything “under the sun”. Nothing satisfied him. The book of Ecclesiastes chronicles his search. He finally concludes, as the verse above testifies, that the whole duty of man is to fear God and keep His commandments.
There are a lot of commandments revealed in the Bible. The most commonly recognized are the Ten Commandments. Jesus summarized those as follows:
Matthew 22:37-39 Jesus said unto him, Thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind. 38 This is the first and great commandment. 39 And the second is like unto it, Thou shalt love thy neighbour as thyself.
Love God and love others. This is the whole duty of man. Notice that there is a priority here. We are to love God first (Matthew 22:38). If we neglect to put God first, we deny ourselves the best He has to offer. Putting God first will beneficially affect the whole of our existence, because we will recognize our utter dependence upon Him and therefore seek His will in our lives, not our own will. This is the whole duty of man.