Sanctification is a gift just as justification is (a double grace, or duplex gratia, as Calvin called it). Both are the gift of God, ours by virtue of union with Christ. Both are found in Christ alone. Both are necessary for salvation – justification being the root and sanctification being the fruit. As is often said: faith alone justifies, but the faith that justifies is never alone. So we must never separate justification and sanctification. The former can’t help but produce the latter, and the latter must flow from the former. And yet we should not be afraid to talk about justification in a different way than we talk about sanctification. One calls us to rest; the other to fight. One reckons us righteous; the other makes us righteous. One allows for no increase or degrees; the other expects progress and growth. One is a declaration of God about us, the other a work of God in us.
Kevin DeYoung