Love.

Whoever does not love does not know God, because God is love. This is how God showed his love among us: He sent his one and only Son into the world that we might live through him. This is love: not that we loved God, but that he loved us and sent his Son as an atoning sacrifice for our sins. … How great is the love the Father has lavished on us, that we should be called children of God! And that is what we are! (1 John 4:8-10; 3:1)