Jesus said, “…you shall not be like the hypocrites.” In this context of prayer, a hypocrite is a man who does not believe in prayer itself but does it to please people so that people can think that he is close to God. It is a form of religious deception. Jesus gave the example of the Pharisees and the Sadducees of His day as a prototype of the hypocrites.
It was not the posture or place of their prayer that was wrong but their motive to be seen by men and to be hailed and praised as somebody who could pray. Jesus said that praise and human applause was their reward. Prayer is a two-way communication between a man and his God for fellowship and for changing situations and circumstances that require divine intervention and divine involvement. You can't afford to pray simply to show off. Some people do so and that is all the reward they will get.
Another problem many believers have with Matthew 6:5 is that in a bid to avoid the rebuke of Pharisees, some believers say, “Well, my prayer is just between me and my God. I'm praying silently in my heart.” That is not what Jesus was saying here. He was neither teaching silent prayer nor praying in your bedroom alone; rather, he was dealing with the motives of the hearts of the people. 
PRAYER: Lord, purify my heart, let it be as gold in Your presence. Deliver me from wrong motives in the place of prayer in Jesus’ name. Amen!
BIBLE IN A YEAR: Numbers 15:17-16:40, Mark 15:1-47, Psalm 54:1-7, Proverbs 11:5-6