CLAIM: Deuteronomy 6:5 states that we should love God with “all your heart and with all your soul and with all your might.” But in addition to these three areas, Jesus adds a fourth. He says, “You shall love the Lord your God with all your heart, and with all your soul, and with all your mind” (Mt. 22:37). Was Jesus adding to Scripture here?
RESPONSE: Even if Jesus was adding to Scripture, so what? The Bible is progressive revelation. By adding “with all your mind,” Jesus could merely be showing an additional commandment from the law that wasn’t originally included in Deuteronomy. This isn’t a case of contradicting Scripture, but adding to Scripture, as all prophets did.
But this solution isn’t necessary, because this fourth area (i.e. loving God with our mind) was implied from the original Hebrew. Poythress writes, “‘Heart’ in Hebrew is not merely the source of emotions, as we tend to think of it in English. It is the center of one’s being. We find in the Old Testament that people think with their heart (Gen. 6:5; Isa. 10:7, ESV; Est. 6:6, KJV; Prov. 23:7, KJV). So Jesus’s citation from Deuteronomy brings out an implication of the verse that is actually there.”
 Poythress, Vern S. Inerrancy and the Gospels: A God-centered Approach to the Challenges of Harmonization. Wheaton, IL: Crossway, 2012. 166.