God, through the prophet Isaiah, made the point that His temple was to be a house of prayer for all nations, and that every aspect of the temple ministry was geared toward that goal. Furthermore, this prophecy, is fully realized in the Church whose members "like living stones, are being built into a spiritual house" (1Pet.2:4-5), in other words, "the temple of the living God" (2Cor.6:16).
Today there are many voices proclaiming what the Church should be or do in the world. Philosophies of ministry and models of doing church are legion - Purpose Driven; Seeker Sensitive; Emergent Postmodern; and, of course the most common, "What we've always done."
But through all this noise the voice of Jesus speaks clearly and simply (though with surprisingly little impact on how the American Church conducts itself), "My house is to be a house of prayer for all nations" (Mark 11:17).
Now again, someone will object to this last comment as being overly critical - "What do you mean 'surprisingly little impact'? Do you mean that our churches don't pray? I can think of a dozen occasions in the last month where prayer was offered!" That prayer happens in most churches at some time or another is not in dispute. But I don't think most churches pray in the way that makes them a house of prayer in the sense Jesus envisioned.
Let's take an example from the restaurant world. Dr. Greg Frizzell puts it like this, "When you call a place a 'house of something,' you certainly expect that 'something' to be the predominant practice of the establishment." (Quoted in The Prayer Saturated Church, Cheryl Sacks, NavPress: Colorado Springs, 2004, 23). Consider the International House of Pancakes or IHOP. What would you guess their menu is based on - steaks, sushi? Pancakes! It's not that they don't serve anything else, but their menu is based on pancakes. The variety and versatility of pancakes is the engine which creates their identity and drives their business. 
Now if for some reason IHOP began to concentrate on a full steak and seafood menu and the only pancakes you could get were a short stack of buttermilk cakes by special order (I'm getting hungry writing this!), then they've lost their identity as a house of pancakes. Furthermore, IHOP may find that though they may try to diversify their menu, pancakes are still at the core of who they are, and it's likely they will not do a very good job at steaks and seafood - unless they have completely changed who they are.
What's this have to do with the Church? Well, if the Church is to be a house of prayer, then prayer cannot be merely one thing on the menu - an item to be ordered if you happen to be hungry for it on occasion. No! Prayer, for a church that is truly a house of prayer, is the defining ministry of the Church. It is the engine which drives everything the Church does.
"But I thought the engine was the preaching of the gospel!" someone might say. Remember, the gospel is the power of God for salvation of all who believe (Romans 1:16). Those who believe are "living stones being built into a spiritual house" (1Pet.2:4), and that house is to be "a house of prayer for all nations." The Church is to be a house characterized by and saturated with prayer at every level, for all things, at all times. It is this dynamic which in turn brings down true spiritual power for the preaching of the gospel.
