The short answer is no, you aren’t dumb for not fully understanding Kierkegaard. He’s a notoriously difficult writer. There are entire books written and classes taught on how to read his works.

My personal understanding of Fear and Trembling is that is in part autobiographical; the product of Kierkegaard breaking off his engagement with Regine Olsen and then basically becoming an angsty teen over it. Kierkegaard is expressing his own experiences through the book; it’s not written as a strictly academic argument, which can definitely make it feel repetitive at times.

While philosophy is infamous for as you put it, a verbose style of writing, this is far from the full picture. In the field I specialize in at least, modern philosophy papers are highly readable and logical. Kierkegaard’s style is a product of his time period and his own philosophy of existentialism (in addition to the fact that every writer has their own approach and quirks). If you don’t like that style, I promise you that there are many other options.