Joel Beeke in Puritan Reformed Spirituality:
Thus, true believer, you are holy before God in Christ, and yet you must cultivate holiness in the strength of Christ. Your status in holiness is conferred; your condition in holiness must be pursued. Through Christ you are made holy in your standing before God, and through Him you are called to reflect that standing by being holy in daily life. Your context of holiness is justification through Christ; your route of holiness is to be crucified and resurrected with Him, which involves the continual ‘mortification of the old, and the quickening of the new man’ (Heidelberg Catechism, Question 88). You are called to be in life what you already are in principle by grace.