Mass is a ritual where Catholics eat wafers and drink wine, believing they are literally turned into the body and blood of Jesus (transubstantiation is the fancy term for it). This is based upon a difference in opinion as to what John chapter 6 refers to. In the chapter, Jesus emphasized that one must eat His flesh and drink His blood to receive eternal life. Catholics assume that means literally, focusing on verses 53-58 where the emphasis is particularly made. Dissenters would point out Jesus began by saying the work of God is to trust on the One God sent (v. 29), and that He ended by saying it's the spirit that brings life, the flesh/physical profits nothing (v. 63)
However, rather than focusing on so controversial a scripture, I would prefer to bring up another that may be more clear and specific. You see, the end result is that Catholics call Mary "the Queen of Heaven" and practice their religion by eating wafers, drinking wine, and burning incense as part of Mass. What is NOT commonly known is that this is mentioned in the Bible, and was done thousands of years earlier - as an idolatrous practice so hated by God that He destroyed most of the nation of Judah for it.
- Jeremiah 7:18-20 The children gather wood, and the fathers kindle the fire, and the women knead their dough, to make cakes to the Queen of Heaven, and to pour out drink offerings unto other gods, that they may provoke me to anger. Do they provoke me to anger? saith the LORD: do they not provoke themselves to the confusion of their own faces? Therefore thus saith the Lord GOD; Behold, mine anger and my fury shall be poured out upon this place, upon man, and upon beast, and upon the trees of the field, and upon the fruit of the ground; and it shall burn, and shall not be quenched.
- Jeremiah 44:15-30 Then all the men which knew that their wives had burned incense unto other gods, and all the women that stood by, a great multitude, even all the people that dwelt in the land of Egypt, in Pathros, answered Jeremiah, saying, As for the word that thou hast spoken unto us in the name of the LORD, we will not hearken unto thee. But we will certainly do whatsoever thing goeth forth out of our own mouth, to burn incense unto the Queen of Heaven, and to pour out drink offerings unto her, as we have done, we, and our fathers, our kings, and our princes, in the cities of Judah, and in the streets of Jerusalem: for then had we plenty of victuals, and were well, and saw no evil. But since we left off to burn incense to the Queen of Heaven, and to pour out drink offerings unto her, we have wanted all things, and have been consumed by the sword and by the famine. And when we burned incense to the Queen of Heaven, and poured out drink offerings unto her, did we make her cakes to worship her, and pour out drink offerings unto her, without our men? Then Jeremiah said unto all the people, to the men, and to the women, and to all the people which had given him that answer, saying, The incense that ye burned in the cities of Judah, and in the streets of Jerusalem, ye, and your fathers, your kings, and your princes, and the people of the land, did not the LORD remember them, and came it not into his mind? So that the LORD could no longer bear, because of the evil of your doings, and because of the abominations which ye have committed; therefore is your land a desolation, and an astonishment, and a curse, without an inhabitant, as at this day. Because ye have burned incense, and because ye have sinned against the LORD, and have not obeyed the voice of the LORD, nor walked in his law, nor in his statutes, nor in his testimonies; therefore this evil is happened unto you, as at this day. Moreover Jeremiah said unto all the people, and to all the women, Hear the word of the LORD, all Judah that are in the land of Egypt: Thus saith the LORD of hosts, the God of Israel, saying; Ye and your wives have both spoken with your mouths, and fulfilled with your hand, saying, We will surely perform our vows that we have vowed, to burn incense to the Queen of Heaven, and to pour out drink offerings unto her: ye will surely accomplish your vows, and surely perform your vows. Therefore hear ye the word of the LORD, all Judah that dwell in the land of Egypt; Behold, I have sworn by my great name, saith the LORD, that my name shall no more be named in the mouth of any man of Judah in all the land of Egypt, saying, The Lord GOD liveth. Behold, I will watch over them for evil, and not for good: and all the men of Judah that are in the land of Egypt shall be consumed by the sword and by the famine, until there be an end of them.
Mass was a pagan practice long before Christianity ever existed, and an idol called "The Queen of Heaven" was worshiped with it. History indeed repeats itself. God has certainly become no more tolerant of such idolatry than He was then.