I always fall back on this little breakdown of timeless salvation in time:

I was saved from the penalty of sin. This is justification.

I am being saved from the power of sin. This is sanctification.

I will be saved from the presence of sin. This is glorification.

All of this was accomplished in Christ "before the founding of the world!" Yet in the fulness of time, Christ died for the ungodly. And over time I strive to experience that righteousness already achieved, and look forward to that glorious day when I'm freed from sin's presence and the power it exerts on me through the world, the flesh, and the devil.

No Christian who is justified by faith can CONTINUE in sin, although he is capable of it and occasionally falls headlong into some besetting sin until lovingly disciplined by his Father. The difference between the depravity of the unregenerate and that of the regenerate is that the unsaved has no "new nature" to help him overcome sin. He has no desire to even try! The regenerate man may rebel for a time, but the inner man - the "new nature" cannot endure it for long, and from his heart a deep desire and yearning for righteousness forces the regenerate rebel to his knees in repentance.

But while "backslidden," even the regenerate man is capable of the most heinous of sins. It is only by God's mercy that that inner nature holds him back.

The old nature is no less totally depraved after regeneration than it was before the new nature was there. That's all I'm say'n.