Here’s an important summary quote at the end, but I suggest you read the whole thing to see the reasoning that leads up to that conclusion:
The Ninth Circuit’s decision represents an unprecedented judicial intrusion into the foreign-affairs authority of Congress and the president. The stakes transcend this particular executive order and even immigration issues generally. By removing restrictions on standing and other limitations on the exercise of judicial power, the Ninth Circuit would make the courts the ultimate arbiters of American foreign policy. The ruling risks creating both a constitutional and a security crisis. It must be reversed.