Albert Barnes Commentary Deuteronomy 6:5

"and thou shalt love Jehovah thy God with all thy heart, and with all thy soul, and with all thy might." — Deuteronomy 6:5 (ASV)

Since there is but One God, and that God is Israel's God, so Israel must love God unreservedly and entirely. The “heart” is mentioned as the seat of the understanding; the “soul” as the center of will and personality; the “might” as representing the expressions and energies of all the vital powers.

The New Testament itself requires no more than this total self-surrender of one's being to one's Maker (Matthew 22:37). The Gospel differs from the Law not so much in replacing an external and carnal service of God by an inward and spiritual one, as in supplying new motives and special aids for attaining that divine love which was, from the first and all along, commanded as the first and great commandment.