Jesus taught what the Great Commandment was. “You shall love the LORD your God with all your heart and with all your soul and with all your might” Deuteronomy 6:5 (NASB). The second is like it, ‘You shall love your neighbor as yourself’” (Matt 22:37-39). Jesus is really saying in the language of the NT that the second is an extension of the first, a piece of the first. So there are not two great commandments, but one. John also makes our love for God and brother to be of one inseparable piece.
Those who say, “I love God,” and hate their brothers or sisters, are liars; for those who do not love a brother or sister whom they have seen, cannot love God whom they have not seen. The commandment we have from him is this: those who love God must love their brothers and sisters also. 1 John 4:20-21 (NRSV)
