For the word of God is quick, and powerful, and sharper than any two-edged sword, piercing even to the dividing asunder of soul and spirit, and of the joints and marrow, and is a discerner of the thoughts and intents of the heart. - Hebrews 4:12
Matthew 22:37-40: Jesus says, "You shall love the Lord your God with all your heart, with all your soul, and with all your mind". This is the first and greatest commandment.