"And Jesus answering saith unto them, Have faith in God."
Mark chapter eleven is essential in the lives of the disciples of Jesus, for it kept their focus on Him and His teaching. In verses 1-11, Jesus made His triumphal entry into Jerusalem to present Himself as Israel’s Messiah. Immediately following that was Jesus’ lesson of the fig tree (vv. 12-14). Then He cleansed the Temple (vv. 15-19). And following this, He taught His disciples a lesson in faith and prayer featuring a withered fig tree (vv. 20-26).
“And Jesus answering saith unto them,”
That fig tree that Jesus saw and went looking for figs on was doing some “false advertising.” It was the wrong time of year for figs, but there were plenty of leaves, saying that there should be figs also, but when He looked for figs there were none.
“The tree is cursed for its pretense of leaves, not for its lack of fruit; like Israel, it has the outward form but no fruit. In this picture, Jesus warned Israel – and us – of God’s displeasure when we have the appearance of fruit, but not the fruit itself. God isn’t pleased when His people are all leaves and no fruit”  (Guzik).
Peter pointed out the dried-up fig tree as the disciples passed by it. Jesus answered him with a valuable lesson about faith.
Jesus taught that faith is vital in the life of His child. Without it, there is no salvation (Ephesians 2:8-9). Without it, there is no way we can hope to please God (Hebrews 11:6). Jesus is showing His disciples how this miracle with the fig tree was the result of praying in faith. If they, and we, will learn how to trust God in this way, they will watch God hear their prayers also. Please note this was not just any “faith.” This is faith with only one object. It is faith…
Faith that works is a faith that has God as it’s focal point. It is placing our trust, our confidence, our dependence upon God. He is the only one who can do what is needed. He is the all-powerful One. It’s not about the strength of my faith, it is about the One whom I am trusting in. Let’s listen to and obey Jesus’ words to His disciples that day, “Have faith in God!”
 Guzik, David, David Guzik’s Enduring Word Commentary, the electronic version in eSword.
 In the grammar of the Greek text here, “God” is an objective genitive. He is to be the focus of our faith. It is reliance upon Him, and not anything else. See Robertson.