Is it necessary to season a cast iron dutch oven before using for the first time?

After the first seasoning, the cast iron will be ready to use and the patina (black natural non stick coating) will continue to build. If you care for the pan properly, you won't have to re-season it. But if you scratch off the patina (in the dishwasher or with a scouring pad), or you notice rust. You will need to re-season it. If it's rusting, you will need to scrape the rust off first.