WASHINGTON — At Chief Justice John G. Roberts Jr.’s confirmation hearings 14 years ago, the first dozen questions were about whether he would respect the Supreme Court’s abortion precedents. He was still answering those questions Thursday night.

In a surprise move, the chief justice joined the Supreme Court’s liberal wing in a 5-to-4 decision blocking a Louisiana law that could have severely restricted abortion in the state. Although he offered no reason for his vote, there is little doubt that he wanted to avoid sending the message that the court was ready to discard a 2016 decision, a precedent, in which it struck down a similar Texas law.

But the court’s order was just three sentences long, and the stay it imposed was temporary. The case is likely to reach the court on its merits next term. And when that happens, it is hardly certain that Chief Justice Roberts will vote to strike down the Louisiana law.

The seeming inconsistency is the result of competing impulses. Chief Justice Roberts is a product of the conservative legal movement, and his general approach is to lean right. But he is also an institutionalist and a guardian of his court’s legitimacy, meaning he wants to make modest and deliberate moves.