the question should be, What is vain repitition?
Matthew 6
5And when thou prayest, thou shalt not be as the hypocrites are: for they love to pray standing in the synagogues and in the corners of the streets, that they may be seen of men. Verily I say unto you, They have their reward.
6But thou, when thou prayest, enter into thy closet, and when thou hast shut thy door, pray to thy Father which is in secret; and thy Father which seeth in secret shall reward thee openly.
7But when ye pray, use not vain repetitions, **as the heathen do: for they think that they shall be heard for their much speaking. **
8Be not ye therefore like unto them: for your Father knoweth what things ye have need of, before ye ask him.
9After this manner therefore pray ye: Our Father which art in heaven, Hallowed be thy name.
10Thy kingdom come, Thy will be done in earth, as it is in heaven.
11Give us this day our daily bread.
12And forgive us our debts, as we forgive our debtors.
13And lead us not into temptation, but deliver us from evil: For thine is the kingdom, and the power, and the glory, for ever. Amen.
lets look at the background,
1 Kings 18:22-40 (King James Version)
22Then said Elijah unto the people, I, even I only, remain a prophet of the LORD; but Baal’s prophets are four hundred and fifty men.
23Let them therefore give us two bullocks; and let them choose one bullock for themselves, and cut it in pieces, and lay it on wood, and put no fire under: and I will dress the other bullock, and lay it on wood, and put no fire under:
24And call ye on the name of your gods, and I will call on the name of the LORD: and the God that answereth by fire, let him be God. And all the people answered and said, It is well spoken.
25And Elijah said unto the prophets of Baal, Choose you one bullock for yourselves, and dress it first; for ye are many; and call on the name of your gods, but put no fire under.
26And they took the bullock which was given them, and they dressed it, and called on the name of Baal from morning even until noon, saying, O Baal, hear us. But there was no voice, nor any that answered. And they leaped upon the altar which was made.
27And it came to pass at noon, that Elijah mocked them, and said, Cry aloud: for he is a god; either he is talking, or he is pursuing, or he is in a journey, or peradventure he sleepeth, and must be awaked.
28And they cried aloud, and cut themselves after their manner with knives and lancets, till the blood gushed out upon them.
29And it came to pass, when midday was past, and they prophesied until the time of the offering of the evening sacrifice, that there was neither voice, nor any to answer, nor any that regarded.
30And Elijah said unto all the people, Come near unto me. And all the people came near unto him. And he repaired the altar of the LORD that was broken down.
31And Elijah took twelve stones, according to the number of the tribes of the sons of Jacob, unto whom the word of the LORD came, saying, Israel shall be thy name:
32And with the stones he built an altar in the name of the LORD: and he made a trench about the altar, as great as would contain two measures of seed.
33And he put the wood in order, and cut the bullock in pieces, and laid him on the wood, and said, Fill four barrels with water, and pour it on the burnt sacrifice, and on the wood.
34And he said, Do it the second time. And they did it the second time. And he said, Do it the third time. And they did it the third time.
35And the water ran round about the altar; and he filled the trench also with water.
36And it came to pass at the time of the offering of the evening sacrifice, that Elijah the prophet came near, and said, LORD God of Abraham, Isaac, and of Israel, let it be known this day that thou art God in Israel, and that I am thy servant, and that I have done all these things at thy word.
37Hear me, O LORD, hear me, that this people may know that thou art the LORD God, and that thou hast turned their heart back again.
38Then the fire of the LORD fell, and consumed the burnt sacrifice, and the wood, and the stones, and the dust, and licked up the water that was in the trench.
39And when all the people saw it, they fell on their faces: and they said, The LORD, he is the God; the LORD, he is the God.
40And Elijah said unto them, Take the prophets of Baal; let not one of them escape. And they took them: and Elijah brought them down to the brook Kishon, and slew them there.
It is vain because they are not praying to the true God, they are praying to Baal.
And, yes I continued to quote the Lord’s Prayer because it is said often in protestant churches.