Love God and love your neighbor
Asked which commandment was greatest, Jesus quoted the command to love God from Deuteronomy and joined it to Leviticus's command to love one's neighbor.
Hear, O Israel: The LORD our God, the LORD is One. And you shall love the LORD your God with all your heart and with all your soul and with all your strength.
Do not seek revenge or bear a grudge against any of your people, but love your neighbor as yourself. I am the LORD.
Deuteronomy 6:4-5 commands wholehearted love for the LORD, and Leviticus 19:18 says to love one's neighbor as oneself. Jesus quotes both in Matthew 22:37-39 and Mark 12:29-31.