Jesus' teaching in this section of the Sermon on the Mount repeatedly emphasizes that the depraved state of the human heart keeps us from coming into God's presence. Likewise, the same depraved nature keeps us from genuine prayer. The only path to genuine prayer is the same path to genuine salvation. It is through the sacrifice of Jesus Christ himself that we can know how to pray.
We are reminded in Psalm 34:45 that "The eyes of the Lord are upon the righteous, and His ears are open unto their cry." Since God's ears are open to only the cries of the righteous, it is then imperative for the heart of genuine prayer be that of righteousness. Faith in the atoning work of Jesus Christ is the only path to righteousness.
Jesus emphasizes in this passage of scripture that the hypocrites pray with 'vain repetition.' But we must also admit that the faithful Christian can sill fall into this trap of vain words in prayer. When one prays in this manner, it is evidence of a lack of genuine faith that our Father in Heaven is actually listening much less will reply with an answer. Instead, Jesus calls upon the citizens of the Kingdom of Heaven to pray in such a way as faith directs the dependence upon God for the words and the heart necessary for genuine prayer.