“By one sacrifice he has made perfect forever those who are being made holy” (Heb 10:14). This verse joins two ways of thinking about the cross of Christ. One is to stress that Jesus has died for me and completely dealt with the problem of sin forever. It’s a done deal!
Of course, we know that is true, but if you push the point too far without any qualification, it sounds as if you just don’t have to try to live a moral life anymore! It is as if it’s given you a clear field to do whatever you like, and God will cover it. It’s like having a rich daddy who’s going to bail you out of trouble every time you crash the Ferrari. (Ah, you had a dad like that too, right?).
The other way is to stress the bit by bit, getting better and better, trying hard each day to live a good life. The trouble with that is it can turn a matter of “It’s just me, trying my best.” But that’s not grace at all, is it? So in this wonderful verse, the two sides of the coin are brought right back into one grace-reality. By the one sacrifice of the cross he has completely dealt with the issue of sin forever (Justification) for those who are “being made holy” (Sanctification). You see, the only basis for the second (Sanctification) is not self-help and effort, but the first (Justification). It’s BOTH AND.