I have come to understand my prayer as having more do to with my faithfulness, my constancy, my determination (I mean it in the sense of prioritizing, not of will-power, though some is required to put prayer first).
Probably, from God's perspective, there is no 'point' in my petitions - He already knows what I am praying for, why, and much more besides, including why He can/cannot honor my prayers as I ask them, but can instead offer me something else much better in the Big Scheme (which may feel a lot less or worse in my small schemes).
But prayer is not about God being changed. It is about me. It is my way of being open(ed). When I pray I change. It is that simple. And if I need to pray about one issue over and over, then I am being changed through that one issue, at ever deeper levels.
There are three changes which are wrought by prayer:
1) the development of my capacity to be reliable - praying daily teaches me to be constant in a world of inconstancy, there is something about the drip-by-drip approach to Heaven. There is no discernible, dramatic, life-altering, apocalyptic change. Just a voice in a corner of a room, in the corner of a street, in the corner of a neighborhood, in the corner of a town, in a corner of the world reciting a psalm very slowly;
2) prayer teaches me to develop patience - in a world of urgency I am reciting my prayers slowly and methodically and, well, prayerfully (lectio, reciting the psalms, etc). There is just no way out of this. You cannot rush through lectio, or it ceases to be lectio. You can say the psalms faster than one of those cattle auctioning guys, but it is no longer a recitation. Furthermore, and the psalms are the primary vehicle for this, the listening again and again to a limited series of problems (David feels cheated or betrayed, the nation of Israel is misbehaving again, God is wonderful and very very scary - did I cover them all?) has developed in me a greater capacity to listen to other people. The sad and sobering truth is that we tend to live our lives playing just one or two notes over and over again. It is a very hard thing to be able to "sing a new song";
3) the tree of constant & patient prayer gives the most succulent fruit of trust - I surrender more and more of my cares to God, and this means that my practice has a causal relationship to how calm, serene, peaceful and joyous I am even in the midst of tribulation. The ceaseless praying of every one of my needs and concerns and fears and pains and angers and lusts and desires and pettinesses and greeds as they happen, even as I am committing them....this raising up the common elements of my life, my bread and wine, so they become His Body and Blood.
It is better to understand the value of the repetitiveness of prayer by doing your own lectio on Luke 18:1-8. It will no doubt open up to you much better and practical and personal insights than the stuff I wrote above.
