John marvels at the love the Father has bestowed on us, that we should be called children of God, and such we are. What we will be has not yet appeared, but when Christ appears we will be like Him, and everyone who has this hope purifies himself. Paul adds that God works all things together for good for those He called, and that He predestined them to be conformed to the image of His Son, the firstborn among many brethren.
The lesson then draws John’s line between the children of God and the children of the devil: the one born of God does not go on practicing sin, and whoever does not practice righteousness or love his brother is not of God. Like Father, like son: we are to be imitators of God, loving even our enemies, for God is love. The Spirit bears His fruit in those who belong to Christ, a tree is known by its fruit, and pure religion cares for orphans and widows.