15 And I, being fifteen years of age and being somewhat of a sober mind, therefore I was visited of the Lord, and tasted and knew of the goodness of Jesus.
Joseph Smith was 14, Mormon was 15, Jacob in the book of Mormon was "in his youth" and they report being visited by the Lord. Such visits are what make scriptures scriptures. The age of the three mentioned didn't necessarily limit a visit from the Lord. Mormon says he was of a "sober mind". He could value the experience and hold it in a place of sacredness. The verse just before this was all about his surrounding environment. Even though what prevailed around him was wickedness, unbelief, and iniquity, Mormon was still visited by the Lord.
Joseph Smith reported "my mind was called up to serious reflection and great uneasiness; but though my feelings were deep and often poignant..." I see something in common with Mormon. Their internal state is able to ponder, reflect, and value something given to them.
When I read that Mormon, Jacob, Nephi, Lehi, Alma...and Joseph and many many others were visited of the Lord, something about that speaks very deeply. This kind of talk is almost totally absent in our day. However the scripture authors were not shy about it. They, as we know, would not profane the sacred, but neither was their testimony put away in hiding. Their testimonies and sacred history are before us all in the scriptures, for believer and Non believer alike.
Mormon says he tasted and knew of the goodness of Jesus. It was a personal, and direct experience. Joseph Smith said it left him with indescribable peace. It all speaks to the fruit Lehi and Nephi spoke of in vision. It's the most pure, and desirable above all else - to quote Nephi and Lehi.
The goodness of God leadeth to repentance and to life (see Romans 2:4).
The goodness of Jesus. How few words could ever attempt to describe that. Mormon's enduring testimony is one that D&C 76, and 138 speaks of. It speaks of a testimony that is tied directly to those who will have eternal life. (John 17:3)
Jesus, the very thought of thee
With sweetness fills my breast;
But sweeter far thy face to see
And in thy presence rest.
-Saint Bernard of Clairvaux