One of the most obvious messages is the old one about not judging a book by its cover. The initially somewhat shallow and inexperienced Leo has an idealized image in his head as to what kind of woman he'd like to marry. It's only when he experiences the crushing disappointment of his big date with Lily that he realizes just how shallow he's been in his search for a mate. Leo finally understands that it's what's on the inside that really matters. If he's going to get married, then it must be to a woman he can truly call his soul mate. That means paying less attention to outward appearance and concentrating instead on the inner goodness of the soul. Now that he knows what he wants from a future wife—love and companionship, rather than social prestige—Leo makes a beeline for Stella, despite her less than savory reputation.

The ending of “The Magic Barrel” demonstrates a couple of lessons.  First of all, love is not always redemptive.  At the end, Leo marries the girl Stella because, “he pictured, in her, his own redemption” and she might love him.  Leo has proven to be very shallow throughout the story, wanting to marry only pretty and young girls.  Leo begins to hate himself, and realizes how bad he sounds.  When he realizes what Stella is (a prostitute), he still decides to marry her.  He is marrying her because of her checkered past, not in spite of it.

Another lesson is that religion should not be used as a crutch.  Leo uses the fact that he is going to be a rabbi and it will be easier to get a congregation if he is married as a reason to go with the matchmaker instead of doing the difficult work of love.

They had made, if not a financially profitable marriage…at least a successful one in the sense of their everlasting devotion to each other.

Leo seems to think that this is what will happen for him.  In the end, although Stella might love him, he marries her because he thinks it will redeem her and in redeeming her it will redeem him.