1 John 3 tells us how to love one another as sisters and brothers in Christ and continues to admonish us to righteousness.
"Little children, let no one deceive you. He who practices righteousness is righteous, just as He is righteous." 1 John 3:7
Here John is reminding us not to be fooled by the Great Deceiver, not to follow the ways of the world and think that we can "get away" with living in sin. God calls us to perfection, to be constantly maturing and walking with Him.
John also defines love for us as children of God...
"By this we know love, because He laid down His life for us. And we also ought to lay down our lives for the brethren." 1 John 3:16
Again, he is calling us to strive for righteousness in that Jesus laid down His life for us, we should do the same for others. Note he does not say we should "be willing to lay down our lives", he says we "ought to lay down our lives". God calls us to put aside our own desires and needs and live for Him and for others.
John ends this chapter with another one of God's many promises...
"Now he who keeps His commandments abides in Him, and He in him. And by this we know that He abides in us, by the Spirit whom He has given us." 1 John 3:24