Albert Barnes Commentary Mark 12:30

"and thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind, and with all thy strength." — Mark 12:30 (ASV)

And thou shalt love. If Jehovah was the only God, then they should not love any other being supremely. Then they should not bow down before any idol. They were required to love God above all other beings or things, and with all the faculties of their minds.