This is the third part of the incident centering on the cleansing of the temple (cf. vv. 12-14).
11:20-21 This event happened on Wednesday morning. "Withered from the roots"means that death was spreading through the tree beginning from its sources of nourishment. The roots of the tree correspond to the religious leaders of the nation. Death would pass from them to that whole generation of unbelieving Jews. Peter connected the judgment with Jesus' words. Likewise Jesus' word of judgment on that generation of Jews would have a similar effect.
11:22-23 Rather than explaining the symbolic significance of the cursing of the fig tree Jesus proceeded to focus on the means by which the miracle happened. This was an important discipleship lesson that Jesus had taught before (cf. Matt. 6:13-14; 7:7; 17:20; 18:19; Luke 11:9; 17:6), but it appears only here in Mark. The point was that dependent trust in God can accomplish humanly impossible things through prayer (cf. James 1:6).
God is the source of the power to change. Moving a mountain is a universal symbol of doing something that appears to be impossible (cf. Zech. 4:7). Jesus presupposed that overcoming the difficulty in view was God's will. A true disciple of Jesus would hardly pray for anything else (Matt. 6:10). The person praying can therefore believe that what he requests will happen because it is God's will. He will neither doubt God's ability to do what he requests, since God can do anything, nor will he doubt that God will grant his petition, since it is God's will.
Why did Mark not explain what Jesus assumed, namely that disciples would pray for God's will to happen? Evidently when he wrote, his original readers were committed Christians. The Roman empire then weeded out simply professing Christians much more than is true today, at least in the West. The idea that a Christian would want anything but the will of God to happen was absurd in a world where identifying oneself as a Christian meant severe persecution and possibly death.
11:24 Asking is a particular form of praying. Disciples can believe we have what we request in prayer when we ask for God's will to take place (Matt. 6:10; 7:7) because God will accomplish His will.
11:25 Faith in God is not the only condition for answered prayer. One must also forgive his or her fellow human beings. The Jews commonly stood when they prayed (cf. 1 Sam. 1:26; Luke 18:11, 13). Forgiving our brothers and sisters is a precondition for obtaining family forgiveness from the Father (Matt. 6:14-15). This is the only place in Mark where Jesus referred to the disciples' Father in heaven. This may have reminded them of His teaching in the Lord's prayer (Matt. 6:9-15).
11:26 This verse does not appear in the most important ancient manuscripts of Mark's Gospel. Evidently scribes inserted it later because they associated the preceding verse with Matthew 6:14.
