How amazing would it be if the bishops could order the trees around and be obeyed? Who would doubt the reality of the Christian religion if such miracles could be performed on a regular basis? But Jesus does not tell the Apostles this fact about trees out of curiosity. They said to him, “Increase our faith!” He did not at that moment work a miracle. He did not have the Father speak from a cloud. He just told them this little fact about mulberry trees.
I think of it like this: if I said to a basketball star, “Increase my basketball skills”, and he told me that if I had just a tiny fraction of the skills of an NBA star, I would be able to slam dunk the basketball, that would increase my desire for the skills, which is sort of the same thing. I would begin practicing harder. I would know that my work is not useless. The Apostles clearly have a desire for faith, which is why they say to Jesus, “Increase our faith.” Jesus, by his words, increases their desire for faith, and since God desires to give us faith the only thing missing is our desire to receive it.
The miracle that Jesus names here is a silly miracle, to replant a tree in the sea, but it is the perfect example because of the diversity of miracles that the Apostles would work. This silly miracle is a symbol of every miracle that the Apostles will work, once their faith has been increased. If Jesus spoke to each Apostle individually, he would have been able to name the miracles they would do once they had faith. If Jesus spoke to us individually, he could tell us what sort of miracles we would be able to do if we only followed him more closely.
I do not put in the effort required to be an NBA star, partly because I believe that no matter how much effort I put in, it would never happen. But I do know that God has plans for me, and I know that those plans are a very real possibility. When I consider what I know of those plans, my heart is on fire to fulfill them. When I spend time in prayer considering the promises of God, even a silly promise like this one about replanting trees, I want to become the person that he knows I can be.