This initial TRO (temporary restraining order) is basically a 14-day pause while other stuff continues before the Court.

Oversimplified, the Plaintiffs basically go "Hey! Someone is doing a thing that we have a problem with! You need to stop them from starting, as the very act of starting causes us harm, in the legal sense of the word." The Judge will eventually grant a fuller ruling, but the back and forth takes a while to make sure everyone doesn't have to rush. The TRO is put in place to buy that time.

To grant a TRO, there are a few requirements that must be met.

• Likelihood of success on the merits (Does the Plaintiff have a reasonably good argument)
• Likelihood of Irreparable Harm (If the TRO isn't granted, will harm occur that can't be undone. For example, once a building is torn down, it's already gone.)
• Public Interest (Do the public's interests align with the Plaintiff)
• Balance of Equities (Is the TRO not unreasonably unfair to one side or the other)

The Judge's decision is 33 pages long, and is based on various factors from several months of litigation on the topic. It's a little long, but pretty easy to parse. If you're inclined to read for yourself, there's a link in the article. The TL;DR is that D.C., Virginia, a Vietnam Vets group, and a couple other interested parties all have various oppositions to the arch due to economic, traffic, safety, historic, etc. claims. Their harm is material, imminent, and frankly, the Government did a shit job of defending themselves.(A few days ago they went "But national security! It's to protect the President!" and refused to elaborate.) So, the TRO is in effect.