Legal authority of the President comes 1. the First Amendment, 2. the Ninth Amendment 3. 18 USC §247. Damage to religious property; obstruction of persons in the free exercise of religious beliefs
18 USC §247. Damage to religious property; obstruction of persons in the free exercise of religious beliefs
(a) Whoever, in any of the circumstances referred to in subsection (b) of this section-
(2) intentionally obstructs, by force or threat of force, including by threat of force against religious real property, any person in the enjoyment of that person's free exercise of religious beliefs, or attempts to do so;
https://uscode.house.gov/view.xhtml?req=granuleid:USC-prelim-title18-section247&num=0&edition=prelim
If 2 months of self isolation, wearing face masks and social distancing do not prevent people without the virus from spreading the virus,
then the emergency decree is repugnant.