What does Mark 11:23 mean?

If the withered fig tree is an illustration of the coming destruction of the temple, then Jesus' side-track into faith seems random. But it's not. The temple has been the focal point of communion with God, and atonement for sin, for hundreds of years. This changes with the resurrection, resulting in faith in Christ bringing complete forgiveness of sins (Ephesians 2:8–9).

The mountain Jesus is indicating is probably the Mount of Olives which sits east of the Temple Mount, across the Kidron Valley. This peak is nearly 300 feet, or 91 meters, higher than the temple. The "sea" is less identifiable. Jesus most likely means the Dead Sea, visible fifteen miles south of the Mount of Olives. Of course, any of these choices would be miraculous. Jesus may be referring to the prophecy in Zechariah 14:1–5 that says at the end of the tribulation, the Mount of Olives will split from east to west, and the people will flee Jerusalem through the newly-made valley.

Jesus promises that the disciples' demands will be met if they have suitable faith. "Doubt" is from the Greek root word diakrino. It is the same word James uses when he talks about being like "a wave of the sea that is driven and tossed by the wind" (James 1:6).

This is not a promise devoid of context, however: there are conditions and expectations attached. We must ask for what is in God's will to give (1 John 5:14–15), and we must abide in Christ in order to know what God's will is (John 15:7). If we do so, our desires will match what Jesus wants, making it easy for God to answer our prayers. We must also ask with the right motives (James 4:1–3). If we ask God to provide us with things that will give us worldly pleasures, we are headed toward conflict with Him and others, not answered prayer.