"We know that we have passed out of death into life, because we love the brethren. He who does not love abides in death. Everyone who hates his brother is a murderer; and you know that no murderer has eternal life abiding in him. We know love by this, that He laid down His life for us; and we ought to lay down our lives for the brethren." (1 John 3:14-16)One of the saddest things to me is when we have to convince someone they're saved. Salvation comes with its own set of changes and conditions by which someone ought to know and discern that they have been converted, born again, and saved. While we all have doubts from time-to-time, there are poofs that point to the reality of the change and the salvation that God has wrought in our lives. One of these proofs is love; especially love for the brethren. Jesus told His disciples, "A new commandment I give to you, that you love one another, even as I have loved you, that you also love one another. By this all men will know that you are My disciples, if you have love for one another." (John 13:34-35) Love is the evidence for not only who we are but whose we are and whose life now lives inside us. If the life of the God who is love dwells in us then we ought to shine forth that life in love for other people. If we have been taught and discipled by Christ who loves us then we should become like Him in loving others the same way. Love is both His command and His evidence that we now dwell in the Kingdom of Light.
However, this love is not, or should not be, limited to our brethren. Among the early church it was noticed by the unbelievers of their time that they often gave aid, not only to their own, but to the pagan believers around them; something the pagans themselves were lax to due. In fact, after Rome had taken up Christianity, there was one emperor, Justin the Apostate, who sought a revival of paganism and even tried to infuse some of the christian morals into his pagan religions. "Julian the Apostate, who tried to check the progress of Christianity and to revive paganism by directing the high priest of Galatia, Arsacius, to establish in every town a Xenodochium to be supported by the state and also by private contributions; for, he said, it was a shame that the heathen should be left without support from their own, while 'among the Jews no beggar can be found, and the godless Galilaeans' (i.e. the Christians) 'nourish not only their own, but even our own poor.'" (Philip Schaff, History of the Christian Church, Volume II, Section 100) Even a hater of Christianity could not fail to take notice of their love for one another and for all mankind.
This kind of love that John is referring to is a love that has actions. One cannot lay down his life without taking up actions. It is also a love that is self denying while it looks to the interests of others. Contrary to the philosophy of Ayn Rand, selfishness is not a virtue in the economy of God. Self love is a love that dwells in darkness while love of others dwells in unapproachable light. Those who love God and who have been loved by God, ought to love others as well. This is His command and it is our proof that we are now children of God.