He brings down the Zohar which describes how the prayer of the poor person gathers up everyone else's prayers, envelopes them and ascends to heaven. There, HaShem tells the heavenly court, leave me for I want to be alone with this special precious prayer. Once the court has left, HaShem derives (figuratively) special pleasure from this prayer, and all the other prayers (that had been hidden within it) are revealed (and answered) as well in this special moment.
From here we can see the most valuable prayer comes from the mouth of he who depends totally and utterly on HaShem for every one of his needs. As long as we think we're ok for now, but we need to pray that HaShem should also provide for us tomorrow or next week or next year, we aren't in touch with the fact that this very moment in which we are "ok" is being given to us right now from HaShem, out of His infinite kindness.