(the opening line is just “Call me ishamel”)

To be fair, that’s a pretty heavy line when it’s taken in context.
It tells you a fuckload about the protagonist:

1. He isn’t seeking notoriety or celebrity.
2. He has effectively nothing to his name, to the point he is comfortable discarding it and starting anew.
3. He feels he was cast out, and likely feels that his own origins up to that point have been a burden.
4. He’s got guts, or courage, or verve, or cojones, or whatever you want to call it- even if you are destitute it takes some not insubstantial strength of character to discard your own identity.
5. Ishmael is not his original name.
6. He is at least moderately educated, literate, and familiar with biblical text in some detail.
7. He has decided he or his descendants may still have some grand future ahead of them, he hasn’t given up on the idea that he may be destined for some greater purpose or adventure.
8. He’s no idiot, The context of Ishmael, son of Abraham and Hagar, isn’t obscure or specialized knowledge, but its application as a sobriquet is subtle and clever.