William Burkitt on 1 John 3:4

Whosoever committeth sin, that is, whosoever lives in the allowed commission of it, lives in rebellion against, and in a flat opposition to, the law of God, sin being a transgression of God's law; and such a person as thus commits sin, not only violates the law of God, but also frustrates the death of Christ; for Christ, in whom there was no sin, was manifested in the flesh to take away sin, the guilt of it by his blood, the power of it by his Spirit, and consequently we must purify ourselves from it, if we hope to see him as he is.

Learn hence, That nothing can be more unreasonble and absurd, than to expect salvation with God in heaven by a sinless Saviour, if we allow ourselves in a course of sin; nothing being more contrary than this to the design of Christ's death, which was not only to deliver us from the danger, but from the dominion of our sins; not only to expiate our sins, but to make us sinless like himself.