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: this is the first commandment.
Cross-references
Deuteronomy 6:5
Citation
Deuteronomy 6:5 is the original command to love God wholeheartedly, which Jesus quotes here.
Psalm 103:1
Parallel
Psalm 103:1 calls for wholehearted praise with all one's being, paralleling the command to love God with all your strength.
Matthew 22:37
Parallel
Matthew 22:37 records the same great commandment in the parallel Gospel account of this conversation.
Luke 10:27
Parallel
Luke 10:27 records the same great commandment in the parallel Gospel account of this conversation.
Micah 6:8
Related theme
Micah 6:8 summarizes God's requirements (justice, mercy, humility) — complementing the total devotion to God commanded here.