Transubstantiation is one of the many false doctrines of the corrupt Roman Catholic Church which was declared an article of faith by the Council of Trent. According to this erroneous belief, the bread and the wine used in the Catholic Eucharist actually becomes the real Body and Blood of Jesus Christ, although not in taste or appearance, after they have been consecrated by the priest. This basically amounts to cannibalism and the drinking of blood; both of which are condemned in the Bible. As Swiss Reformer, Ulrich Zwingli, and other 16th century Reformers sought to prove, Christ's reference to eating His Flesh and drinking His Blood, was only meant to be understood in a symbolic sense; that is, communion serves as a symbolic commemoration of Christ's Sacrifice, our belief in it, and our spiritual union with Him. This is why the Lord Himself says in the Book of Revelation:
"Behold, I stand at the door, and knock: if any man hear my voice, and open the door, I will come in to him, and will sup with him, and he with me."
Revelation 3:20, KJV