In Mark 11:23-24 we read, "I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." On the face of it, this verse seems to be saying that God will grant literally any request we make of Him as long as we believe.
However, it is important to recognize that there are limitations on what God will give -- which is indicated both by the context and by other texts, as well as by the laws of God's own nature and the universe.
First of all, God cannot literally give us anything. Some things are actually impossible. For example, God cannot grant a request of a creature to be God. Neither can He answer a request to approve of our sin. God will not give us a stone if we ask for bread, nor will He give us a serpent if we ask for fish (see Matthew 7:910).
Second, all passages should be interpreted in harmony with other clear statements of Scripture. As an illustration, it is clear that God does not promise to heal everyone for whom we pray in faith. Paul wasn't healed, though he prayed earnestly and faithfully (2 Corinthians 12:89). Jesus taught that it was not the blind man's lack of faith that hindered his being healed. Rather, he was born blind "that the works of God should be revealed in him" (John 9:3). Despite the apostle Paul's divine ability to heal others (Acts 28:9), later he apparently could not heal either Epaphroditus (Philippians 2:25) or Trophimus (2 Timothy 4:20). It clearly was not unbelief that brought Job's sickness on him (Job 1:1).
Finally, when the rest of Scripture is taken into consideration there are clear conditions placed on God's promise to answer prayer in addition to faith. We must "abide in Him" and let His Word "abide in us" (John 15:7). We cannot "ask amiss" out of our own selfishness (James 4:3). Furthermore, we must ask "according to His will" (1 John 5:14). Indeed, on all except God's unconditional promises, this "if it be your will" must always be stated or implied.
