N.T. Wright is Professor of New Testament and Early Christianity at the University of St Andrews in Scotland. This extract is from his article, Justification: The Biblical Basis and its Relevance for Contemporary Evangelicalism, available here.
The positive result of justification is that we live for God because Christ has died for us. Good works, as the Reformers never tired of saying, are done not to earn salvation but out of gratitude for it: not out of fear lest we should be lost after all but out of joy that we are saved after all. Sanctification is the completion, not of justification, but of regeneration: holiness is the continuation and bringing to perfection (in the resurrection of believers) of the good work which God has begun by the new birth. Justification is a different kind of event altogether: regeneration and sanctification are acts of grace to change the heart and life, whereas justification is the declaration, anticipating the verdict of the last day, that the believer is in the right. Justification results in holiness because it presupposes the new birth. It is therefore also the basis of Christian assurance, the certain hope of eternal life. Assurance is not an extra blessing over and above justification, but simply the outworking of justification itself, the realization that the Spirit who inspired faith and now inspires love will continue until, in the resurrection, he has produced the full harvest of which he himself is presently the first fruits.