“Christ is our holiness in the same sense in which he is our righteousness. He is a complete and all-sufficient Savior. He does not rest until, after pronouncing his acquittal in our conscience, he has also imparted full holiness and glory to us. By his righteousness, accordingly, he does not just restore us to the state of the just who will go scot-free in the judgment of God, in order then to leave us to ourselves to reform ourselves after God's image and to merit eternal life. But Christ has accomplished everything. He bore for us the guilt and punishment of sin, placed himself under the law to secure eternal life for us, and then arose from the grave to communicate himself to us in all his fullness for both our righteousness and sanctification.”
(Herman Bavinck, Reformed Dogmatics, IV:248)
And here's another...
“Because sanctification, like the whole of salvation, is the work of God, we are admonished, obliged, to a new obedience, and we are also qualified for it. He grants abundant grace not that we should instantly or suddenly be holy and continue to rest in this holiness, but that we should persevere in the struggle and remain standing. He hears our prayers but does it in accordance with the law and order which He has fixed for the spiritual life. Hence we are always of good course, for He who has begun a good work in us will finish it until the day of Jesus Christ. The believers can and they will become holy because in Christ they are holy.”
(From Our Reasonable Faith, pp 502-3).