This verse is full of encouragement for imperfect sinners like us, and full of motivation for holiness.
It means that you can have assurance that you stand perfected and completed in the eyes of your heavenly Father not because you are perfect now, but precisely because you are not perfect now but are “being sanctified,” “being made holy” ? that, by faith in God’s promises, you are moving away from your lingering imperfection toward more and more holiness. That’s the point of Hebrews 10:14.
Does your faith make you eager to forsake sin and make progress in holiness? That’s the kind of faith that in the midst of imperfection can look to Christ and say, “You have already perfected me in your sight.”
This faith says, “Christ, today I have sinned. But I hate my sin. For you have written the law on my heart, and I long to do it. And you are working in me what is pleasing in your sight (Hebrews 13:21). And so, I hate the sin that I still do; and I hate the sinful thoughts that I contemplate.”
This is the true and realistic faith that saves. This is the faith that can savor the words, “By a single offering he has perfected for all time those who are being sanctified.”
This is not the boast of the strong. It is the cry of the weak in need of a Savior.
I invite you, I urge you, to be weak enough to trust Christ in this way.