The evolution of Merry is very much in keeping with Tolkien's careful pen. All of the characters start with not much to go on but native talents and pluck, including Gandalf! It is tempting to think that the Professor drew on his World War I experiences, but he might have used it as more of a template rather than to draw a portrait of the Somme.
What is late adolesence-early manhood than a fair faced youth atop his horse daring the world to unseat him? Well it does and for everyone else too, for Merry is not so unique in his faltering. What comes across here is not the false steps or bad choices, it is the courage to see this task to its end that bares out Merry's noble character. His kindness to Theodin is a comfort of sorts that mitigates some of the loss of the King's son, and that too proves a grand heart. Frailty is not in and of itself a lack of virtue, but is the voice of prudence. Only when one's back is against the wall and all alternatives gone can one strike out with our own small blades and hobble the greatest fearful shadow.
I look forward to the Scouring of the Shire when we discuss the Return of the King in depth, but for now let us say that it is a very important chapeter to display that in our own age, we too must face great peril on our own terms - without wizards or enchanted beings.
Believe and you will find your way
a promise lives within you now