The size of faith doesn't matter because God is the one doing the moving.
If it is my faith that moved the mountain, then the bigger the mountain the more faith I would need to move it.
The bigger the obstacle the more strength I'd need to climb it. The more serious the illness a faith even greater would be required to overcome it. The more serious the sin the more faith I would need in order to have it forgiven.
That kind of thinking kind of makes sense, but that's not how faith works. In fact, faith doesn't do the work at all. And thank God for that.
God is the one doing the work through faith. Think of faith as the key that opens the door to God acting in our lives. If I have a bigger key ring than you do, does it matter? The size of a key ring doesn't matter - key rings don't open doors but it's that little key on the ring that opens doors. Even a little faith opens the door for God to move the mountains and trees and even our hearts.
I once visited on online greeting card website to send an electronic anniversary card to some friends. As I was glancing through the website's menu of choices, I noticed they had a separate category of cards devoted to "Forgiveness." Most of these cards were humorous ones intended to be used for relatively minor hurts. "Forget about it," "Don't worry about it" were the sentiments of two cards. Another expressed forgiveness by saying, "Everybody is a work in progress."
Curiously, forgiveness cards were categorized right along with birthday and get-well cards. That is, they were what could be called "occasional cards." You don't send a "Get Well" card just any old time, but occasionally you need such a sentiment and that's when you purchase and send just such a card. So also, you may not need a forgiveness card very often, but once in a while such a thing may be handy.
Seen this way, forgiveness becomes a "now and then" matter. But it is precisely such an understanding of forgiveness that the New Testament calls us to resist. Forgiveness is an ongoing necessity, and so the church will never be done with needing it. Maybe that is why in that most famous of all prayers, the Lord's Prayer, Jesus puts the need to forgive hard on the heels of the request for daily bread. Have you ever thought of that? The request for bread and the plea for forgiveness are yoked with the word "and." "Give us this day our daily bread and forgive us our sins as we forgive the sins of others." You say these two petitions in the same breath. Why is that important? Because perhaps it is Jesus' way of telling us that there is a connection between daily bread and forgiveness--we need both every day!