God's people love one another, and that love is patterned after the love that God has shown toward us. This love rises above anything that the world demands or offers. It is a love that is fashioned by the experience of being loved by God in Christ.
It is grounded in what God's people are to God, what God's people are in themselves, and what God's people are to us. It is manifested in sincere and sacrificial practical expressions of love, being both declared and demonstrated. It is essentially corporate: the church is the natural sphere in which such love shows itself.
If we lack such love, we show that we are not truly children of God. If we have a nature to love and are being nurtured in such love, it shows that we have been born again.