The idea is the courts look to Congress on what is constitutional and they follow its rulings. A court could only declare a law
ultra vires that is, a law that makes something not delegated to Congress by the Constitution. With judicial review gone, all other laws are presumed constitutional and the courts have a manifest duty to uphold them. Nothing circular about it.
(Denny Crane: "Sometimes you can only look for answers from God and failing that... and Fox News".)