I don't think belief in a God/Gods is childish, but I definitely think organised religion, the kind where people gather in church and are "displeased" with people that are homosexual, different religion or sinful, is childish.

As Marcus Aurelius said:

“Live a good life. If there are gods and they are just, then they will not care how devout you have been, but will welcome you based on the virtues you have lived by. If there are gods, but unjust, then you should not want to worship them. If there are no gods, then you will be gone, but will have lived a noble life that will live on in the memories of your loved ones.”

Einstein said the Jews aren't as special as they want to be, each religious group wants to hold onto their unique Us vs. Them mentality and Einstein knew that if the Jews were going to clutch that and not let others hold the same thing they were going to be in for a nasty shock.No surprise that no other religion agrees that Judaism is the one and only path. He was telling them to get out of the way, politely, to let bygones and dead eras flow away. Wash away the sin of being too proud and have humility; piety is great but when piety turns to pride you'll get more than enemies of your friends.

I think Einstein didn't want to end Jewish culture, just make sure it had room at a table for other ideas and religious ideas to be welcomed by Jews.

Jews aren't the only ones waiting for religious heroes, Jews just have different religious heroes.