"And the prayer of faith shall save the sick, and the Lord shall raise him up; and if he have committed sins, they shall be forgiven him." (James 5:15)
Without examining the various interpretations of this somewhat controversial passage, we merely note that one of the main ingredients of effective praying is faith. There are others, of course (praying in God’s will, no unconfessed sin, unselfish motives, etc.), but all these must be "mixed with faith" to be effective (Hebrews 4:2).
There are many such exhortations to pray in faith. Jesus said: "All things, whatsoever ye shall ask in prayer, believing, ye shall receive" (Matthew 21:22). Another example is James 1:5-6: "If any of you lack wisdom, let him ask of God, that giveth to all men liberally, and upbraideth not; and it shall be given him. But let him ask in faith, nothing wavering." And another: "Therefore I say unto you, What things soever ye desire, when ye pray, believe that ye receive them, and ye shall have them" (Mark 11:24).
Every Scripture passage must be viewed in context, of course, including the context of the entire Bible. The "faith" we must exercise is not only a spiritual confidence that God will answer (and this, clearly, is necessary), but also faith in God as Creator (and, therefore, able to answer!), Christ as Savior (therefore, justly willing to hear), and in the Holy Scriptures as the written Word of God. James warns any man without genuine faith: "Let not that man think that he shall receive any thing of the Lord. A double-minded man is unstable in all his ways" (James 1:7-8).
True biblical faith is faith in God the omnipotent Creator (Hebrews 11:3), faith in Christ as redeeming Savior (John 3:16-18), and obedient faith in the revealed Word of God (1 John 3:22). Then we can believe in confidence that God will indeed answer our prayer of faith. HMM