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If the prayer of one righteous person praying earnestly in faith in accordance with the will of God is effectual, then one would think that to have more people praying would have its impact on the heart of God as our heavenly Father. However, there is no passage that directly states this, that I can recall.
We are told that where two or three are gathered together in Christ’s name (Matt. 18:20), there He is in a special way in their midst. Though this passage is not dealing with corporate prayer in general, but is stated in relation to the issue of church discipline, it may provide some insight on this question. We also see that Peter was released from prison as a result of the corporate prayer of the church in Acts 12:5. In Matthew 21:22, the promise there is in the plural, “all things whatsoever you (pl) ask in prayer believing (pl. participle), you (pl) shall receive.