Mark 12:29

And Jesus answered him, The first of all the commandments is, Hear, O Israel; The Lord our God is one Lord:

The Speaker is Christ Himself, who first uttered these words to ancient Israel from the cloudy pillar and spoke them again when the Word was made flesh and dwelt in the world, repeating them to teach men how to be saved. He spoke them as His answer to the scribe's question about which is the first commandment of all, proclaiming to Israel that God is one Lord. The one Lord is identified as Israel's God, and His unity is declared, meaning there is one God and there is none other but Him.

That declaration that the Lord God is one stands first among all the commandments. It introduces the first and great commandment, the first principle of God's law, which requires supreme, wholehearted love for God with all the heart, soul, mind, and strength. The whole heart, soul, mind, and strength belong to Him, for the Lord is one. Hearing Israel's declaration that the Lord is one is joined to loving Him thus.

This command to love God sums up the first four of the Ten Commandments, which express that love and define duty to God, while love for neighbor as self sums up the last six. Together Christ joins them into one divine whole, held together by love to God and love to neighbor, a sacred unity that cannot be ranked or divided. The law is therefore not a collection of commands that can be ranked or ignored, so that breaking any one violates the principle of love, and love for God is shown by obedience to all His commandments. The first four are not more important than the remaining commandments in a way that excuses neglect of duty to others.

Love for one's neighbor follows from, flows from, rests on, and is founded on supreme love for God and cannot be separated from it. Giving God His rightful place in the heart leads to treating one's neighbor rightly and makes impartial love for others possible. These two commands together sum up the law and the prophets, and all the law and the prophets hang on them. Together these principles express the unity of God's law. They are greater than all other commandments and more than all burnt offerings and sacrifices.

Love for God and love for neighbor are immutable principles, as eternal as God's throne, by which character is tested and obedience is shown. Supreme love for God shows that truth is an abiding principle in the mind and heart. True obedience is faith working by love that purifies the soul, gives God the whole service He requires, and pours out goodness, love, and compassion toward others, rather than merely acknowledging truth or performing ceremonies and sacrifices. The verse is a rule given by Christ that those who claim to be converted must keep in practical life, with every church member pledging in the presence of God and fellow believers to strictly obey it together with wholehearted love for God and love for neighbor as self. Discreet acceptance of this truth places a person not far from the kingdom of God.