Marin ell is one of the strangest characters in the whole Faerie Queene. It's never clear exactly what he represent (except being associated with the sea) and his sudden turn from violent, sworn bachelor to husband of the sought-after Florimell is extremely quick and kinda mysterious.
What Marinell's marriage does show us is the poem's constant emphasis on the benefits of romance and marriage. Even though Marinell's mother received a prophesy that said her child would be seriously hurt by a woman—and instructs her baby boy never to love—love overcomes all and Marinell ends up getting hitched. If even Marinell, the woman-averse loner, can end up finding true love, then love must be pretty great.