Christians are called to love each other. But what is love? You might know it when you see it. Specifically, John says that our model is Jesus: 

We know love by this, that He laid down His life for us (1 John 3:16a). 

Love is sacrificial. Love acts. It acts for the good of the beloved. Jesus showed you that He loves you by dying for you. 

Jesus does not only show that He loves us, He also shows how you should love others: 

and we ought to lay down our lives for the brethren (1 John 3:16b). 

You are called to love like Jesus, laying down your life for the brethren. But what does that mean? Is John being literal? For example, does he literally want you to be crucified for other people? No. The crucifixion is a one-time event (Rom 6:10). 

Does John mean we should be martyred for other people? Possibly. It is possible you might one day be put in a situation where you might literally give your life for another person. Read the news, and you’ll find people who jump onto train tracks to save a child who has fallen in. Or they take a bullet for a friend. Or die protecting a stranger. Pregnant mothers have foregone taking chemotherapy to save their children.

That said, I think John has a much more “everyday” application of what it means to lay down your life for the brethren. He explains it in the next verse: 

But whoever has the world’s goods, and sees his brother in need and closes his heart against him, how does the love of God abide in him? (1 John 3:17). 

John is arguing from the greater to the lesser. 

The greater is laying down your life, i.e., physically dying for another. If you’re willing to do that, then you should also be willing to do the lesser thing, i.e., sharing your material possession with the poor. That’s the application. That’s what “laying down your life” looks like in everyday situations. If you see a brother in need, you should love him by sharing your material possession with him. You should not shut up your heart against him but love him through concrete actions. Laying down your life is sacrificial. So is sharing your material possessions with people in need. 

The greater involves sacrificing your life. The lesser involves sacrificing the luxuries of life to meet someone’s necessities of life. 

If that sounds challenging, it should. John didn’t say loving is easy. But it is necessary for Christian maturity. Don’t shut your heart to that message!