If God has preordained everything and already made up His mind about how things will be, why do we pray for other people in intercession? It just doesn't seem to make sense that we should ask God to do things for other people if He never changes his mind!My response:
I know that prayer is important for communicating with the Lord, so that we draw closer to Him, and acknowledging His sovereignty, but why should we go to Him in supplication for other people if He already knows what we want and what He will do? Is the prayer itself preordained?
Great question to be thinking about! Check out this article from John Piper.
I'll answer it first in terms of praying for someone to be saved. The basic answer is that while God ordains the ends (someone's salvation), he also uses means (prayer & a person sharing the Gospel) to accomplish the end. Just like God uses us as messengers to verbally share the Gospel with another person as a means toward that person coming to faith in Christ; likewise, God uses prayer as a means of bringing someone to faith in Christ.
So, for instance in Romans chapter 10 we see these two means put together. In verse 1 Paul says: "Brothers, my heart’s desire and prayer to God for Israel is that they may be saved." (ESV)
Then in verses 14-17 he says:
How then will they call on him in whom they have not believed? And how are they to believe in him of whom they have never heard? And how are they to hear without someone preaching? And how are they to preach unless they are sent? As it is written, "How beautiful are the feet of those who preach the good news!" ....So faith comes from hearing, and hearing through the word of Christ. (ESV)
So, God uses prayer and a messenger to bring about salvation in people's lives.
I think we can also apply this to interceding for other issues as well - that God uses our prayer to help others grow, to bring healing, to convict hearts, to change circumstances, etc. James 5:13-18 helps us to see this truth: Is anyone among you suffering? Let him pray. Is anyone cheerful? Let him sing praise. Is anyone among you sick? Let him call for the elders of the church, and let them pray over him, anointing him with oil in the name of the Lord. And the prayer of faith will save the one who is sick, and the Lord will raise him up. And if he has committed sins, he will be forgiven. Therefore, confess your sins to one another and pray for one another, that you may be healed. The prayer of a righteous person has great power as it is working. Elijah was a man with a nature like ours, and he prayed fervently that it might not rain, and for three years and six months it did not rain on the earth. Then he prayed again, and heaven gave rain, and the earth bore its fruit. (ESV)
James makes it clear that God uses prayer as a means of accomplishing his purposes. The cool thing is that he uses us and our prayers to do it! I think it's fair to say that the more we pray, the more we will be used by God and see him work. The less we pray, the less we will be used and see him work.
Obviously we shouldn't and can't use prayer as a tool to manipulate things, but instead see it as a partnership with God where he wants to use us. We're his messengers, his servants, his prayer warriors, and he is using us to do his will on this earth.
Now, the details of exactly how that all works, well, there is definitely some mystery involved there!
Hope this helps.