Please read the passage before that the homily.
If you had owned a millstone in the ancient world, you would have owned a very valuable piece of equipment. It was designed to make processing grain into flour more easily and readily. Were one to tie a millstone around a person’s neck and throw that person into sea, you would be using a very expensive means of executing someone.
On the other hand, forgiving other people is possible, even to the nth degree, whether that symbolic number is seven. Seventy-seven or the nth time. Giving scandal is a horrible offense and a sin, which may deserve an expensive means of execution, but it is also possible to forgive such a sin, even for the nth time.
The Apostles wanted to have their faith increased. This too is a mighty work, like forgiving to the nth degree or using an expensive means of execution. Increasing faith is so big and hard that it only requires faith the size of a mustard seed, nothing more and nothing less: it is the biblical smallest seed.
We celebrate the power and mercy of God. Scandals can come, but we can overcome them. Forgiveness of sins and faults is possible, not once, but always. Growing in faith is filled with hope because it only takes a small amount of faith, less than the size of a small seed, for faith to move trees and mountains.
There may be evil and sin in the world, but there is abundant forgiveness and a growing faith. The world is already redeemed, and God can see this growth. In faith we can see the growth too.