Recently, someone asked me about praying according to God's will. This person understood that it is appropriate to pray, "Lord have mercy," when you don't know what God's will is. But what if you think you do know what God's will is, or this person asks, "Can you ever know what God's will is in a specific situation?" The specific example of praying for someone dying of cancer was given.
Questions like these do not have easy answers. Questions like these reach to the core of who we are as human beings, who God is (as far as we can know Him) and what our relationship with God is. These are the kind of questions one spends a whole lifetime pondering because as our knowledge of God and ourselves increases so does our perception of the depth and breadth these questions touch on.
Nevertheless, rushing in where Angels fear to tread, I tried to provide an initial response to these questions. Below is what I wrote.
It is a yes and no sort of thing. Discovering the will of God is something that we spend our life doing and is seldom known in advance, and when it is known in advance, it is with a large amount of uncertainty (that is, you only realize that you knew it after the fact--and even then we don't know anything that we think we know as we ought to know it [cf 1 Cor. 8:1-2]). The best we can do is say something seems to be God's will. The problem is that we tend to think that something (some choice or circumstance of life) either is or isn't God's will. But I think God's will has to do much, much more with issues of character and spiritual growth than it has to do with whether A or B happens.
Everyone dies. Much more important than when one dies (this year by cancer or a few years from now by a heart attack or car accident or thirty years from now with Alzheimer's) is one's state before God and with his or her fellow human beings when he or she dies. And this is something only God knows. We pray that God would have mercy. We pray for what we want to happen, too; but at the same time we know that we do not know what is best. We know that our own fears, doubts, cultural prejudices, and general selfishness and ignorance all play into what we want to happen--and even (maybe especially) into what we think God's will is.
Miraculous healing is a sign. It is a sign to strengthen the faith of the one healed and those nearby. But still, everyone miraculously healed still has to get sick and die again (or die one way or another). St. John Chrysostom said that when God heals someone (and this is not uncommon in the Orthodox Church), God removes one cross to give them a heavier cross. Suffering—of any kind--is part of our sharing in the sufferings of Christ (and thus sharing in His Resurrection), if we offer our suffering to God in faith.
We are so blind and confused. We want certainty. We want to know whether A or B is God's will. But we are dealing with God here, not our limited perception of reality that reduces reality to concepts and categories that are easy for us to understand. God's will may have nothing (or very little) to do with A or B, but probably has everything to do with how you trust in God and grow into the likeness of Christ and love our sick friends regardless of whether A or B or C or D happens.