Of the Fall of Man, of Sin, and of the Punishment Thereof, VI:5

This corruption of nature, during this life, remains in those that are regenerated; and although it be, through Christ, pardoned, and mortified; yet both itself, and all the motions thereof, are truly and properly sin.

Being spiritually regenerated in Christ by the Holy Spirit does not remove the old sin nature from a Christian. "The old man dies hard." The new nature in Christ wars against the old nature and gradually gains ground, although the old nature remains present throughout this life. The Christian's sins are pardoned and guilt is removed and the sin nature "mortified," to use the language of the Confession. We are called daily to strive toward holiness, even to be holy just as our Father in heaven is holy. But there will always have to be vigilance against sin and the danger of falling back into it for a season. Entire sanctification is not realized until heaven. Those who think otherwise (and I saw the website of one such just today) are greatly mistaken.

And sin remains sin, whether committed by a believer or unbeliever.

Tomorrow: The outworkings of sin.