Whatever value is indeed received in the works of sanctification by those who trust in Christ, it is accrued to them not by the spirituality or devoutness of their own righteous deeds, but rather on the basis of God's gratuitous grace. And I might add that the grace of God in both our justification and sanctification in Christ is received solely by faith alone.
"In one word, as we said of man, so we may say of works: they are justified not by their own desert, but by the merits of Christ alone; the faults by which they would otherwise displease being covered by the sacrifice of Christ. This consideration is of very great practical importance, both in retaining men in the fear of God, that they may not arrogate to their works that which proceeds from his fatherly kindness; and also in inspiring them with the best consolation, and so preventing them from giving way to despondency, when they reflect on the imperfection or impurity of their works, by reminding them that God, of his paternal indulgence, is pleased to pardon it."
-The Necessity of Reforming the Church (1543), John Calvin.