Then Jesus told his disciples a parable to show them that they should always pray and not give up. He said: "In a certain town there was a judge who neither feared God nor cared about men. And there was a widow in that town who kept coming to him with the plea, 'Grant me justice against my adversary.'In our world of weights and measures, blame and finger-pointing it is so very, very easy to view our Lords justice in a similar fashion. Then by extension we treat our relationship with Him with the same lopsided scales we use in our relationships with others.
"For some time he refused. But finally he said to himself, 'Even though I don't fear God or care about men, yet because this widow keeps bothering me, I will see that she gets justice, so that she won't eventually wear me out with her coming!' "
And the Lord said, "Listen to what the unjust judge says. And will not God bring about justice for his chosen ones, who cry out to him day and night? Will he keep putting them off? I tell you, he will see that they get justice, and quickly. However, when the Son of Man comes, will he find faith on the earth?"
-- Luke 18:1-8
There is no requisite number of prayers, there is no magic measure of faith, there is no transaction that can be constructed, no matter how ambiguously that will influence the will of our Father. People aren't saved because we prayed 400 times instead of 399. Prayer is not a hand grenade or a game of horse-shoes. It is not a game, not a purchase, not a currency.
At least one point for this parable is to show us that our God who IS just is so vastly different then our human measures. The judge in the parable is wicked; he only helps the widow to shut her up! My Father hears every utterance of my mind, each time, every time, regardless of the atrocious weakness of my faith.
All this is not to discourage our devotion to prayer. Absolutely not! At the conclusion of the parable we are reminded that the Son of Man will come and will then determine if He finds faith on earth. One of the greatest expressions of our faith is prayer. This is why we are commanded to always pray and not give up. When the Lord returns he will find us praying without ceasing.
More than just diligent obedience it is worth remembering that prayer is one of the most tangible ways our faith is exercised. It is our conversation with our Lord, the way we build our relationship with our Father. Not as a currency, not for a transaction or to bring influence. Simply because there is no place we'd rather be than conversing with our Savior, especially in those moments of hurting.