Thank you for your comment.
>Why does he sit up there all day?
That's a big question. Up is his choice I think.. but sit is for meditation. Buddhist monk meditates in search of truth, to experience the truth themselves for Nivarana.
Easier way for us to understand meditation would be, "why one eats? It’s for physical well being. Also one meditate for mantel well being." People sometime take vacation to get away from stress build up in work-life and etc. When meditation is done properly, it brings calmness, tranquility, peace and wisdom.
Hope that help. For certain thing, one must experience to understand, like falling in love or swimming.