It's never a good sign when the caption and official summary of a Ninth Circuit opinion goes on for 13 single-spaced pages. Indeed, the actual opinion itself isn't much longer than that.
Fortunately, I can save you the trouble of reading the whole thing. Just skip to page 14. Judge Friedland there tells you all that you basically need to know about today's holding:
"When a federal regulation is challenged in court, the promulgating agency may ask the court to remand the regulation to the agency for an opportunity to reevaluate it and correct any errors. Courts often grant such voluntary remands without ruling on the lawfulness of the challenged regulation. The question we face today is whether a court granting a voluntary remand may also vacate the regulation without first holding it unlawful, as the district court did here. We hold that courts lack the authority to do so, and we therefore reverse."
Sure, you can wade through the whole thing if you'd like. But that's a very good articulation of the basic deal.