Good hymn writing takes skill and patience. Writing a strong melody that is memorable and matches the lyrics but stays in a tight meter and form is downright difficult. Add to that, creating an underpinning of harmonies with an interesting chord progression (which cannot be too predictable) following all of the Rules of Proper Voice Leading, then the task becomes even harder. And in the end, the hymn just has to be enjoyable to sing. Good hymns are difficult to write.
It can be baffling to contemplate why we like what we like and dislike vehemently what doesn't work for our ears or our hearts. Some of our favorite hymns are deceptively simple. The melodies seem like they just always existed because they fit the text so well. The meters, rhythms, rhyme schemes, motives, and word painting all come together so seamlessly that they are always thought of together. And how can a melody so interesting and beautiful be underpinned by just three chords? 'Tis a puzzlement, for sure!
I do hope that the young composer will take more time to study part-writing for SATB Mixed Chorus so that when he revises his hymn, it will work beautifully