The Roman Catholic Catechism still teaches and affirms prayer to Mary and invocation of the saints for help (see paragraphs 2675, 2676, 2683, 956, etc.). In Protestant theology, specifically in the Reformed catechisms, prayer to Mary and to the saints is said to be idolatry – a violation of the first commandment. Why or how is prayer to saints or Mary (or anyone besides God) a form of idolatry and a grave sin? Charles Hodge explains this well as he gives three main theological objections to the invocation of saints (I’ve slightly edited the following for length):
1) It is, to say the least, superstitious. It assumes, without any evidence from Scripture or experience, that the spirits of the dead are accessible to those who are still in the flesh; that they are near us, capable of hearing our prayers, knowing our thoughts, and answering our requests. The Church or the soul is launched on an ocean of fantasies and follies, without a compass, if either suffers itself to believe without evidence; then there is nothing in astrology, alchemy, or demonology which may not be received as true, to perplex, to pervert, or to torment.
2) The whole thing is a deceit and illusion. If in fact departed saints are not authorized and not enabled to hear and answer the prayers of suppliants on earth, then the people are in the condition of those who trust in gods who cannot save, who have eyes that see not, and ears that cannot hear. That the saints have no such office as the theory and practice of invocation suppose is plain, because the fact if true cannot be known except by divine revelation. But no such revelation exists. It is a purely superstitious belief, without the support of either Scripture or reason. …If this be so, then how dreadfully are the people deluded How fearful the consequences of turning their eyes and hearts from the one divine mediator between God and man, who ever lives to make intercession for us, and whom the Father heareth always, and causing them to direct their prayers to ears which never hear, and to place their hopes in arms which never save. It is turning from the fountain of living waters, to cisterns which can hold no water.
3) The invocation of saints as practiced in the Church of Rome is idolatrous. Even if it be conceded that the theory as expounded by theologians is free from this charge, it remains true that the practice involves all the elements of idolatry. Blessings are sought from the saints which God only can bestow; and attributes are assumed to belong to them which belong to God alone. Every kind of blessing, temporal and spiritual, is sought at their hands, and sought directly from them as the givers. This Bellarmine (a Roman Catholic theologian) admits so far as the words employed are concerned. He says it is right to say: “Holy Peter, save me; open to me the gates of heaven; give me repentance, courage,” etc. God alone can grant these blessings; the people are told to seek them at the hands of creatures. This is idolatry. Practically it is taken for granted that the saints are everywhere present, that they can hear prayers addressed to them from all parts of the earth at the same time; that they know our thoughts and unexpressed desires. This is to assume that they possess divine attributes. In fact, therefore, the saints are the gods whom the people worship, whom they trust, and who are the objects of the religious affections.
covenant presbyterian church (OPC)