One must love God with the heart. "With all thy soul" includes all of one's spiritual nature; "with all thy mind" means that all of the intellectual powers must be brought into subjection to the truth of God.
He meant that one must surrender his entire being to the will of God and use the faculties of his being to promote the honor and glory of God. This statement of the law includes the four commandments which were inscribed on the first table of stone, which regulated man's conduct toward God. Man's duties to God come first; they are supreme and must have the right of way in every life that would enjoy God.
Jesus did not stop with that commandment, but added that "a second like unto it is this, Thou shalt love thy neighbor as thyself." This is a summary of the six commandments on the second table of stone of the Decalogue, which describe and regulate man's conduct toward his fellow man. In these two summaries Jesus covers the entire law, and said, "On these two commandments the whole law hangeth, and the prophets." All things in the Old Testament dispensation proceed from these two laws; all things that Moses and the prophets wrote were intended to bring men to the supreme principle of love to God and to man. In one sweep Jesus includes the entire will of God as revealed to man, and shows that no one section or clause of it can be disregarded or exalted above another. They recognized that Jesus had answered "discreetly" and no one of them asked him any more questions. Luke 20:40.
When people do not with the soul desire above all things to do the will of God, they do not love him. To love thy neighbor as thyself is not to feel a magnetic attraction toward him, but it is to have the purpose of heart, soul, and mind to do him good, to work for his happiness and well-being as we labor for our own well-being and happiness. He is a true child of God who is willing to sacrifice every fleshly feeling and impluse and bear all things to do the will of God. He loves his neighbor as himself who can choke back the angry feeling and forget wrongs suffered in order to benefit and help him. We can wisely love self only by loving the neighbor.
—Gospel Advocate Commentaries