C.S. Lewis and others on prayer

Another text that I have been working through on the topic of Christian prayer is a collection of letters that C.S. Lewis wrote to a friend, Malcolm, clustered around the topic of prayer. They were published in a book, Letters to Malcolm: Chiefly on Prayer, initially recommended to me by a thoughtful friend (thanks, Steve).
One of the things I have found interesting while contemplating this subject is how nearly every writer or thinker I have encountered takes up, at some point, the question of God's foreknowledge and prayer. Origen is pithy on this point, noting that one might well object to prayer, seeing as how it is an awful lot like beseeching God that the sun might rise in the morning. If God has perfect foreknowledge and if God is providential, what happens is inevitable, and what purpose then do our prayers serve?
A more existential way of putting this paradox was summed up in the lyrics to an old Caedmon's Call song, "The Close of Autumn" I believe was the title:

All this time I've been thinking, wondering how would it be
To breathe in deep
Guess I need to be careful when I ask for a drink
Just might get what I ask for
And I know just what you'd say to me
That's why I don't ask you
What would I ask you

My dad has often quoted that last line, "what would I ask you," wondering why we pray.
There are a couple of layers to this. First, when we pray we often already know the answer God will give. Which of you if his son asks him for bread would give a stone? And yet, which of you if his son asks for poison would grant his request? Secondly, why do I ask when God presumably already knows not only just what he'd say to me, but also just what I'd ask of him?
It is almost a given that Christian writers taking up the subject of prayer will address this question at some point, yet it is fascinating that they often come at the question from different angles. Origen takes a number of angles, but starts with a philosophical argument: while God might have perfect knowledge of the future, that does not mean that his knowledge is itself the cause of any particular future event. For us then, it is important that we pray because our will is the cause of such events and God simply knows if we will chose to pray or not.
This is an interesting enough argument, but fairly abstract. Augustine takes a different angle:

But it is because the act of prayer clarifies and purges our heart and makes it more capable of receiving the divine gifts that are poured out for us in the spirit. God does not give heed to the ambitiousness of our prayers, because he is always ready to give to us his light, not a visible light but an intellectual and spiritual one: but we are not always read to receive it.

From this angle, the effect of prayer on God is not the primary issue but rather the effect of prayer on the one offering it up. This is classic Augustine and a beautiful twist in addressing an age old question. God is always already answering us, but we are not always ready to receive.
Lewis' take gets a little closer to answering the question as posed by the Caedmon's Call lyric, taking a more relational and existential approach. Borrowing a page from Martin Buber Lewis suggests that regardless of whether or not God has perfect foreknowledge or determines all things, God desires us to pray to him because it places us in a dialogical relationship with God. Without prayer, Lewis writes that God's knowledge of us is like his knowledge of any other object: "We are, like earthworms, cabbages, and nebulae, objects of Divine knowledge" (Lewis, p. 33). It is only when we pray to God that we become something other than mere objects of knowledge, like those cabbages and nebulae. In Buber's words, when we pray the relationship God has with us switches from merely an I-it relationship to an I-Thou relationship. Through prayer we offer God our subjectivity.
Once again this has me thinking about parent and child, or two lovers or any other persons locked in a relationship for that mater. In our most intimate human relationships it is still important to speak words, ask questions, vent at the end of a long week, even when (and perhaps most crucially when) we already know what will be said or what will be answered.
Take the words "I love you." When spoken truthfully and without guile these words are often anticipated, expected, foreknown even; just as much as the reply, "I love you too."