In the first reading we are invited to return to God. We must return to the Lord, though we have sinned against him. We return to God in humility, the creature to his Creator. We return to God by praising him for his compassion and forgiveness.. And we resolve that our only God is Yahweh, not any of the many false gods. And God promises to love us in return.
In the Gospel reading Jesus re-affirms the commandments, “The first is: Hear; Israel! The Lord, our God, is One Lord; and you shall love the Lord, your God, with all your heart, with all your soul, with all your mind and with all your strength. And after this comes another one: You shall love your neighbor as yourself. There is no commandment greater than these two.” (Mk 12: 29- 31)
God is a jealous God: he cannot allow other gods. Love of neighbor is a necessary extension of love of God: after all, love is simply putting others before ourselves and the readiness to give ourselves for the good of others.