"And when you are praying, do not use meaningless repetition as the Gentiles do, for they suppose that they will be heard for their many words. "So do not be like them; for your Father knows what you need before you ask Him. (Matthew 6:7-8 NASB)
In the previous verses we see Jesus warning against praying in public to be seen by other people, and it is clear that praying is not a performance. Moreover we recognized that the prayer which is most pleasing to the Lord is that which takes place in total privacy never to be seen by anyone else except the Lord. Now as we enter into this passage we see that mere privacy does not negate hypocrisy in prayer. You could still enter into a private room and hit your knees with nobody knowing it and yet remain inhypocrisy. Look at this passage, 'do not use meaningless repetition'. This is an important warning, and it speaks hard against the countless 'hail Marys' and rosary prayers that are repetitions without meaning. However it is more than that, it speaks against the same meaningless repeated dinner prayers, or night time prayers. 'for they suppose that they will be heard for their many words' many times people will believe they have a firm foundation because 'they say their prayers' but their prayers are the same meaningless repetitions from the day before, and their consistency in this does not earn them any place with the Lord. Hypocritical prayer turns devotion to the Lord into a mere repetition, or devotion to a prayer or prayer time. We must go even further here, there are many who attempt to get into a prayer mode by repeating a mantra over and over again 'come holy spirit, come holy spirit...' or something like that. This idea of repeated chanting of a prayer will certainly cause things to happen in your mind, and even create sensations that seem supernatural but it is vain repetitions toying with the natural functions of the human brain. The word is clear, avoid meaningless repetition, your Father knows what you need before you ask Him. The final warning is that you will not be 'heard for their many words.' Prayer is more about devotion than duration. Now listen, you ought to pray for long periods of time, this is a good practice, but when you have spoken to the Lord your desires and devotion you do not need to drag out words upon words somehow believing if you use enough words He will hear you. Much of prayer is silent, offering God a still mind, speaking as the words come, not forcing the issue.
Now with this all said, there is a discipline required for prayer. Setting aside specific time each day to be alone in prayer is essential to the Christian life. Rigid discipline in your life is encouraged in the scriptures, and evidenced by Christ. This passage speaks nothing against discipline, and it is not an open endorsement to just float around and wait for the spirit to tell you what to do and what to say. At the same time praying is not to be a ritualistic repetition, and if the entirety of your praying is ritual and repetition this passage is calling out your hypocrisy.