If I could I would throw out the verse about praying in the closet because of our obsession with individualism. You and I aren't likely to stop praying our private prayers. Those are the ones that are comfortable and convenient. It is the praying with others that we resist and rarely do. But if we take Jesus at his word that is when he is present, when we are together.
Christian prayer is always communal prayer.
When we pray alone we do that as an extension of the community. In the strictest sense there is no such thing as private Christian prayer. Christ always puts us firmly in the community. We need the time for personal prayer everyday, but it needs to be in tandem with communal prayer. The two go together and you can't have one without the other.