"But if any of you lacks wisdom, let him ask of God, who gives to all men generously and without reproach, and it will be given to him. But he must ask in faith without any doubting, for the one who doubts is like the surf of the sea, driven and tossed by the wind. For that man ought not to expect that he will receive anything from the Lord, being a double-minded man, unstable in all his ways." - James 1:5-7
Many Christians are confused about what it means to "pray in faith" for something. The passage quoted above, as well as Jesus' words in Mark 11:20-27 concerning mountain-moving faith, lead them to conclude that they may pray for anything at all, and receive it, so long as they believe, without any doubting that it shall come to pass. Yet they know that it also says that we must pray according to the will of God if our prayers are to be answered (1 John 5:14-15). "So which is it;" they wonder, "may I pray for anything I want and get it so long as I believe it will come to pass, or must I know first that it is the will of God?" In other words, whose will has the final say in this matter?
The first thing to notice is that if we go with the first answer, that we may pray for anything at all and so long as it is prayed in faith, without any doubting, it will be done, then we are really not doing what Jesus and James are telling us to do in the first place - "have faith in God. (Mark 11:22)" Our faith in that case would be faith in our faith. So long as we can summon enough faith we know our prayer will be answered. But that is like trying to lift yourself up by your own bootstraps!
No, we must keep our eyes upon God in all our prayers and expectations. God has revealed certain things as always His will. James mentions wisdom. We may know for certain that it is always God's will for us to have the wisdom we need to lead a holy life, pleasing to God and helpful to our fellow creatures. We are beset by many stratagems and schemes of the devil. The flesh can lead us astray, along with the influence of the ungodly or spiritually immature. To keep on the path that is pleasing to God, we need wisdom to tell truth from error, right from wrong, love from selfishness and the harmful from the beneficial. We even need wisdom to distinguish the best from the merely good. Do you think it would ever be God's will for you to be fooled into sin? Of course not! God's whole purpose is to make us holy, to help us conform to the image of His beloved Son. To doubt this is to doubt that God is holy and that is a prayer-spoiler if there ever was one. To ask God for wisdom to lead a holy life and avoid sin and not be thoroughly confident that He will give you as much wisdom as you need is blasphemy!
But there are things that we might not immediately know to be God's will. How do we pray in faith for these things? The circumstance that usually sparks this question is a health problem, whether it involves a debilitating condition or something that threatens death. There are many Christians that are convinced that the Bible reveals that it is always God's will to provide physical healing. I have read a number of books and heard many sermons by people who hold to this view, and I must say that I respect their opinions. Still, I remain to be convinced. I could go over the verses, pro and con, but there is one basic reality that withstands their best arguments: saint and sinner, we are all under sentence of death and if accident or homicide don't take us out, disease will, certainly. Aging is a disease process. If the theory of those who believe it is always God's will to heal and always our duty to believe that He will, were true, then everyone of them lacks faith in God for they too grow old, get grey hair, lose their 20/20 vision and fall prey to the diseases of aging.
We look forward joyfully to the redemption of our bodies (Romans 8:23). We shall, one day, have bodies that do not decay or die, nor will they suffer weariness or pain. We shall have glorified bodies as Jesus has had since His resurrection from dead. In the meanwhile "we groan within ourselves, waiting eagerly for… the redemption of our bodies." God does heal us in our present, fallen condition, using means both natural and supernatural. It is perfectly right and proper to pray for healing. I think God would be disappointed if we didn't ask, but He alone knows if it would be wise to grant our prayer.
To pray in faith for healing, therefore, consists in two things. First, when we pray for healing we are to have faith that God will, if it is His will, answer our prayer. Second, we must have faith that if He doesn't see fit to answer our prayer, He is still good, wise and just. On the other hand, there are cases where God reveals to us that it is definitely His will to heal in this particular instance. This is what we might call the "gift of faith" and is referred to by Paul in 1 Corinthians 12:9 and 13:2. It is to be distinguished from the "fruit of faith" (verses 7, 13) which a Christian is to exercise at every moment. The gift of faith is where God informs us directly that it is His will to answer a particular prayer, or make good our command, as He did for Jesus when Jesus cursed the fig tree. In such cases, though, the principle of God's will being the determining factor still applies, as with ordinary prayer.
The conclusion is, therefore, that we must always pray in faith. When we know that it is God's will, we must believe He will do it. If His will is not known, we must believe that He will do it, if it is His will, and that if He doesn't answer our prayer, He remains absolutely good and worthy of our full confidence. As Job said, "Though He slay me, yet will I trust in Him." (Job 13:15)