"I am sending you to them to open their eyes, in order to turn them from darkness to light, and from the power of Satan to God, that they may receive forgiveness of sins and an inheritance among those who are sanctified by faith in Me." (Acts 26:17b.-18) because many are hindered by their own ignorance and malice, that they cannot reap such fruit of the gospel as they ought, we must note this description, which sets before our eyes briefly and plentifully that incomparable treasure. Therefore, this is the drift of the gospel, that being delivered from blindness of mind, we may be made partakers of the heavenly light; that being delivered from the thraldom of Satan, we may be turned to God; that having free forgiveness of sins, we may be made partakers of the inheritance among the saints. Those which will rightly profit in the gospel must direct all their senses to this end; for what good shall the continual preaching thereof do us, if we know not the true use thereof? Also, the way and means to attain to salvation is described to us, all men boast that they be desirous of salvation, but few consider how God will save them.

Therefore, this place, wherein the means is prettily comprehended, is, as it were, a key to open the gate of heaven. Furthermore, we must know that all mankind is naturally deprived of those good things which Christ says we have by believing the gospel; so that it follows that all are blind, because they be lightened by faith; that all are the bond-slaves of Satan, because they are set free by faith from his tyranny; that all men are the enemies of God, and subject to eternal death, because they receive remission of sins by faith. So that nothing is more miserable than we, if we be without Christ, and without His faith, whereby it appears how little, yea, that nothing is left for the free will of men's merits. As touching every part, this lightening is referred unto the knowledge of God, because all our quickness of sight is mere vanity and thick darkness, until He appear unto us by His truth. That reaches farther which follows afterward: To be turned from darkness to light; for that is when we are renewed in the spirit of our mind.

Therefore, in my judgment, this member, and that which follows, express both one thing, to be turned from the power of Satan unto God. For that renewing which Paul declares more largely in the second chapter to the Ephesians, (Ephesians 2:10, and Ephesians 4:23) is expressed in divers forms of speech. Remission of sins follows next, whereby God doth freely reconcile us to Himself, so that we need not doubt but that God will be favorable and merciful to us... by faith we come unto the possession of all those good things which are offered by the gospel. And faith is properly directed unto Christ because all the parts of our salvation are included in Him. Neither doth the gospel command us to seek the same anywhere else save only in Him.

~ John Calvin. Commentary on Acts 26:18