As a young Protestant, this was one of my favorites to ask Catholics. “Why do Catholics pray ‘repetitious prayer’ like the Rosary when Jesus says not to pray ‘vain repetitions’ in Matthew 6:7?”
I think we should begin here by quoting the actual text of Matt. 6:7:
And in praying do not heap up empty phrases (“vain repetitions” in KJV) as the Gentiles do; for they think that they will be heard for their many words.
Notice the context? Jesus said “do not heap up ‘empty phrases’ (Gr. –battalagesete, which means to stammer, babble, prate, or to repeat the same things over and over mindlessly) as the Gentiles do…” We have to remember that the main idea of prayer and sacrifice among the pagans was to appease the gods so that you could go on with your own life. You had to be careful to “take care of” all of the gods by mentioning them, and saying all the right words, lest you bring a curse upon yourself.
And remember as well, the gods themselves were immoral at times! They were selfish, cruel, vengeful etc. The pagans would say their incantations, offer their sacrifice, but there was no real connection between the moral life and the prayer. Jesus is saying that this will not cut it in the New Covenant Kingdom of God! One must pray from a heart of repentance and submission to God’s will. But does Jesus mean to exclude the possibility of devotions like the Rosary or the Divine Mercy Chaplet which repeat prayers? No, he does not. This becomes evident when in the very next verses of Matthew 6, Jesus says:
Do not be like them, for your Father knows what you need before you ask him. Pray then like this: Our Father who art in heaven, Hallowed be thy name. Thy kingdom come. Thy will be done, on earth as it is in heaven. Give us this day our daily bread; And forgive us our debts, As we also have forgiven our debtors; And lead us not into temptation, but deliver us from evil. For if you forgive men their trespasses, your heavenly Father also will forgive you; but if you do not forgive men their trespasses, neither will your Father forgive your trespasses.
Jesus gave us a prayer to recite! But notice the emphasis on living the words of the prayer! This is a prayer to be recited, but they are neither “empty phrases” nor “vain repetitions.” Read the whole article here.