In many areas of constitutional law, the Court allows a constitutional right to be overcome when a restriction passes "strict scrutiny"—i.e. (to oversimplify slightly), when the government can show that restricting the right is the "least restrictive means" of serving a "compelling government interest."
In some fields, such as free speech or race classifications, the inquiry is "strict in theory but [almost] fatal in fact": Very few restrictions pass the test. But in other areas, such as religious exemptions governed by RFRAs or RLUIPA (statutes that borrow the strict scrutiny test from constitutional law), a lot of restrictions must pass—no Justice thinks, for instance, that people should get religious exemptions from laws banning homicide or theft or vandalism or trespass, or for that matter from most tax laws and other important regulatory regimes. At the same time, a lot of others should fail. The details of how strict scrutiny plays out end up being quite important, but while the Court has a lot of precedents applying strict scrutiny, many of the key questions (such as how one can tell whether an interest is "compelling") remain unresolved.
I've long been interested in the subject (see, e.g., my criticisms of strict scrutiny in my 1996 Freedom of Speech, Permissible Tailoring, and Transcending Strict Scrutiny and in Part II of my A Common-Law Model for Religious Exemptions), and I was therefore especially interested in seeing Justice Kavanaugh's concurrence discussing the matter in today's Ramirez v. Collier:
