Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof;
The words "separation of church and state" aren't there. Amendment I doesn't mandate the "separation of church and state." The devout can and do participate in affairs of state to their hearts content. The Establishment Clause of the First Amendment only prohibits laws "respecting an establishment of" one "religion" as the national religion. There's a helluva lot more play in that language than in Amendment II and SCOTUS interpreted the language of Amendment II to confer a right to private firearm possession!
The Court could easily construe the Constitution's actual words in the Establishment Clause as permitting any law of Congress short of making Christianity the official national religion. And in Lemon v. Kurtzman, 403 U.S. 602 (1971) the Court interpreted the language of Amendment II to uphold any law of Congress passed on religion if (1) the primary purpose of the
assistance is secular, and (2) the assistance does not promote or
inhibit religion, and (3) there is no excessive entanglement between
church and state. Those are conjunctive: all three are required. The second prong of the Lemon test has the most bite: thou shalt not "promote" but the actual language of Amendment II was clearer still, and "promote", "primary", and "excessive entanglement" (lol) do not appear in Amendment I either. Lemon was a Roe v Wade-era case. Might today's Jesus, Guns & Babies Court overrule Lemon?