The efficacy of prayer

This past week, I heard two rabbis speaking about the power of prayer. One rabbi related an anecdote about a young boy who had been paralyzed for twelve years and was lying in a hospital bed in Poland. Two of his friends went to collect expenses for his hospital bills and they found themselves at the home of the Chofetz Chaim. They poured out the tragic story to the gadol, whereupon he began to daven for the boy. When the friends returned to Poland, they were amazed to see the boy sitting up in his hospital bed. The rabbi then told us, 'You see, tefilot work." My friend turned to me and said, "The tefilot of the Chofetz Chaim work. But our tefilot wouldn't have worked."
The rabbi must have heard her comment because he said, "You know, we daven veli'Yerushalayim Ircha (And to Jerusalem Your city return in mercy, and dwell within as You promised) and people are discouraged. They think to themselves that if the prayers of the Ari z"l and the Chasam Sofer haven't brought about the redemption, how can our prayers help?"
The rabbi continued, "Imagine a great wall is being built. First, large stones are laid for the foundation. More and more stones are laid atop the foundation until the wall is finally built. So too, the rabbis laid the large stones of the wall with their prayers, whereas we have contributed with our tefilot to the layers on top. At some point, the wall will be finished. Who knows which prayer will constitute the end of the construction of the wall?"
Yesterday, I heard a second rabbi talking about the power of prayer. He said that no prayer is for naught. One might not be answered immediately and it can take even a second generation to see the results of the tears shed by the parents to prove the efficacy of prayer. He related two stories where grandchildren were helped by the prayers uttered by their grandparents years before.
The power of prayer is great. No prayer is for naught.

The video link below is from Tisha B'Av a couple of years ago.

http://www.youtube.com/watch?v=qEgYuLEuO-k&eurl=http%3A%2F%2Fmashiachiscoming%2Eblogspot%2Ecom%2F&feature=player_embedded