Anyone who does not love remains in death. A man who is physically alive knows it from the consciousness of the life itself that is coursing through his veins. Men may try to convince him that he is dead but he knows he is alive. Just so spiritually. The life of love is the life of God, is eternal life.
Selfishness is death.
He knows it by the testimony of the life itself. It is important to notice, however, what God's tests of love are. And so we know and rely on the love God has for us. God is love. Whoever lives in love lives in God, and God in him.