In his Politca methodice digestica1 Johannes Althusius makes the following observation about the spiritual nature of faith, warning the civil magistrate not to assume control over what is solely God’s jurisdiction:
A magistrate in whose realm the true worship of God does not thrive should take care that he not claim imperium over that area of the faith and religion of men that exist only in the soul and conscience. God alone has imperium in this area. To him alone the secrets and intimate recesses of the heart are known. And he administers his kingdom, which is not of this world, through his ministers of the Word. For this reason, faith is said to be a gift of God, not of Caesar. It is not subject to the will, nor can it be coerced. If in religion the soul has once been destroyed, nothing henceforth remains, as Lactantius says. We are not able to command religion because no one is required to believe against his will. Faith must be persuaded, not commanded, and taught, not ordered.2
Althusius goes on to note:
Those who err in religion are therefore to be ruled not by external force or by corporal arms, but by the sword of the spirit, that is, by the Word and spiritual arms through which God is able to lead them to himself. They are to be entrusted to ministers of the Word of God for care and instruction. If they cannot be persuaded by the Word of God, how much less can they be coerced by the threats or punishments of the magistrate to think or believe what he or some other person believes. Therefore, the magistrate should leave this matter to God, attribute to him the things that are his — who alone impels, leads, and changes hearts — and reserve to himself what God has given him, namely, imperium over bodies. He is forbidden in his administration to impose a penalty over the thoughts of men.3
Note Althusius’ careful distinction between the outward coercion utilised by the civil magistrate and the inward work of God to bring people to faith. The spiritual rule of God, whereby he leads people to himself, is not conducted by civil magistrate. Note also that ‘ministers of the Word’ are administrators of ‘his kingdom’, but they do this by the ‘Word of God’ or ‘the sword of the spirit’. So it is God who is ruling directly through his Word. Althusius emphasises very clearly God’s agency in ruling the spiritual kingdom, as He ‘alone impels, leads, and changes hearts’. The civil magistrate and the minister of the Word are not, in any sense, to claim imperium over the conscience. It is God’s alone.