Indwelling sin always abides whilst we are in this world; therefore it is always to be mortified. The vain, foolish, and ignorant disputes of men about perfect keeping the commands of God, of perfection in this life, of being wholly and perfectly dead to sin, I meddle not now with. It is more than probable that the men of those abominations never knew what belonged to the keeping of anyone of God’s commands, and are so much below perfection of degrees, that they never attained to a perfection of parts in obedience or universal obedience in sincerity. And, therefore, many in our days who have talked of perfection have been wiser, and have affirmed it to consist in knowing no difference between good and evil.
Not that they are perfect in the things we call good, but that all is alike to them, and the height of wickedness is their perfection. Others who have found out a new way to it, by denying original, indwelling sin, and at tempering the spirituality of the law of God unto men’s carnal hearts, as they have sufficiently discovered themselves to be ignorant of the life of Christ and the power of it in believers, so they have invented a new righteousness that the gospel knows not of, being vainly puffed up by their fleshly minds. For us, who dare not be wise above what is written, nor boast by other men’s lines of what God hath not done for us, we say that indwelling sin lives in us, in some measure and degree, whilst we are in this world.
– John Owen –
from The Mortification of Sin in Believers, volume 6 of Works, page 10