Suppose if I want someone to read a long essay that would take long get finished, what expression should I write to have patience? Because its worthwile as well.
I assume OP's precise context requires a word to fill the blank...
I'd like you to read my essay. I know it's long, but please ____, because it's worthwhile.
I personally don't think be patient is likely to be particularly suitable there, because it strongly implies the essay will be boring, unsatisfying (until some "punch line" right at the end, which supposedly will justify the entire reading process).
To my mind, please persevere is much better. There's still the implication that reading the essay may1 require effort - but let's face it, great literature is more likely to be called "difficult" than "boring".
1 Note that this is just a possible implication. It's also possible the only reason perseverance might be required is because the reading will take a long time (not that it will be difficult for any other reason).