Now, on His last night on earth, Jesus urges His disciples to carry this love forward. He repeats the commandment (John 15:12–13) and tells His disciples (and us as well) to imitate Him in our love for one another. “I have shown you My love,” He is saying. “Now, you follow My lead. You love one another in the same way.” He is identifying love for others as the trademark of His true disciples. In other words, people will know we are Christians by our love.

Peter, who was present for this discussion, got the point. Later he wrote, “Above all things have fervent love for one another, for ‘love will cover a multitude of sins’ ” (1 Peter 4:8). Peter learned the truth of this verse through a bitter experience he would never forget. In a moment of fear, he denied that he even knew Jesus. The overcoming power of love was driven home when Jesus later sought him out and forgave him.

It’s obvious that Jesus’ command to love one another also deeply impressed John. After reiterating the commandment twice in chapter 3 of his first letter (1 John 3:11, 23), he says in chapter 4, “If God so loved us, we also ought to love one another. No one has seen God at any time. If we love one another, God abides in us, and His love has been perfected in us” (vv. 11–12).

In other words, God is invisible, but His love flowing through us makes His presence tangible to others, much like the rustling of leaves gives tangible evidence to the presence of wind. When we truly love, John says, God lives within us and builds up our capacity for love, making it more powerful and dynamic all the time.

Clearly, Peter and John came away from that evening with Jesus with the impression that love was their lifetime assignment. They were to reach the nations with the message, and love would be the wind that carried it from God to an inattentive world. If we love, it will get people’s attention. If we don’t, they will never listen.

According to John, there is no alternative to love. It is no less than a litmus test for our faith. He who does not love his brother is simply “not of God” (1 John 3:10). Even more clearly, “he who does not love does not know God, for God is love” (4:8). Twelve verses later, unloving believers are called “liars.” Such people are walking “in darkness” (2:11) and abiding “in death” (1 John 3:14).

Loving one another, in other words, is not a discipline reserved for advanced Christians or a gift belonging to naturally tolerant people. It’s not an option or an extra or a frilly wrapping to make religion more attractive. Love is the heartbeat of our faith; and if we detect no pulse, there is no faith.