To John, no doctrine is so high and esoteric that it is useful for nothing except blissful meditation.  Every single doctrine he has in his arsenal is useful in provoking his little children to love and to good works.  Thus he makes a practical application of this cherished hope of the Christian, that he will see Christ as He is, and will be like Him at that day.  Considered only theoretically, one might wonder how this knowledge, delightful as it is, might be used to direct us to good works.  John proves it to be not only possible, but logical, by asserting that every man who possesses this hope, waits not till the end of time to be made like Christ.  He sees the image of Christ now, painted in the narratives of the four gospels, and strives to conform himself to that image.  In the language of our passage, he purifies himself even as Christ is pure.  Christ is our Saviour, but He is also our great example of personal sanctification and wholehearted consecration to the service of God.  We desire to purify ourselves from sin, as did Christ, to love the children of God, and to obey the law of God in all points, even as did our Redeemer.

This matter of purification points us particularly towards abstention from sin.  This is why John proceeds from the example of Christ to point us to the law.  This should not be thought of as an abrupt change of subject, when we considered that our Lord Jesus was “made under the law,” and lived His entire life in subjection to the commandments of God.  Purification from sin always involves the law of God, because sin can only be identified by the law.  This is neatly encapsulated in John’s words, “For sin is the transgression of the law.”  If we would purify ourselves from sin, we must know what sin is.  The only way we can rightly identify sin is by studying the law of God.  A thorough understanding of the divine law will warn us against all things which God would forbid us, and it will also prove a guard against condemning those things which God never condemns.