Even though he was just a young man of fifteen years, Mormon was filled with faith and his life was one of righteousness to the point that he was privileged to see the resurrected Christ. At some point too he was privileged to see and know the three translated Nephites (see Mormon 8:11).
Perhaps even greater than these visitations, Mormon knew the “goodness of Jesus” by personally experiencing the blessing of the Atonement—through faith in Christ he was born again and, being filled with the Spirit, had iniquity burned, as it were, from his soul.
This spiritual transformation from the natural man who is an enemy of God to a “new creature in Christ” is the application of “the goodness of Jesus” we also should seek to know.