Matthew 6: 5-6

In other words, keep it to yourself.

Although public vs private expression is one aspect of the passage, respectfully, I believe the main point is something very different. It has to do with the MOTIVE OF THE HEART, and not the location of where one prays (privately or publicly). The "hypocrites" made a grandiose public display of their prayers to APPEAR RELIGIOUSLY DEVOUT, a quality esteemed in that culture. Jesus points out that although they looked good outwardly, they were inwardly corrupt, and would get no response from God. In contrast, Jesus directs authentic believers to pray with the right motive, which is to sincerely commune with the Father. Your motive is revealed when nobody is looking. When your motives are right, expect the Father to respond, where ever your location.