Since church discipline is of a spiritual nature and, as one of the keys of the kingdom of heaven, has been given to the church to shut and to open that kingdom, the consistory shall ensure that it is used to punish sins against both the purity of doctrine and the piety of conduct, in order to reconcile the sinner with the church and with his neighbour, and to remove all offence out of the church of Christ — which can be done only when the rule given by our Lord in Matthew 18:15-17 is followed in obedience.