1 John 3:1, 10

See what an incredible quality of love the Father has shown to us, that we would [be permitted to] be named and called and counted the children of God! And so we are! For this reason the world does not know us, because it did not know Him.

By this the children of God and the children of the devil are clearly identified: anyone who does not practice righteousness [who does not seek God’s will in thought, action, and purpose] is not of God, nor is the one who does not [unselfishly] love his [believing] brother.