See Leviticus 19 and Deuteronomy 10 regarding the injunction to treat sojourners as your own.
The First Amendment first guarantees freedom
from religion, and then, secondarily, freedom
of religion. (It would have been easy to write it the other way around, but it isn't written that way.) It absolutely means the government cannot promote Christianity, or any sect thereof, or any other religion, or religion generally (or irreligion). Furthermore, one of the US's oldest treaties, which was ratified unanimously by the Senate (
23-0, 9 not voting, so even over the required two-thirds if that had to be an absolute matter) includes in it a clause explicitly stating that the US is not a Christian nation. Many of the people who wrote that document were from Virginia, which itself was actually aggressively secular, and, yes, it was intended to erect a wall of separation between church and state so that no religion could use the government to oppress other religions.
The US Supreme Court has indeed held that Jefferson's writings (in particular, his letter to the Danbury Baptists, who were being persecuted in Connecticut as they were not Congregationalists) "may be accepted as an authoritative declaration of the scope and effect of the [First] Amendment." (
Reynolds v. U.S., 1879.) However, at the time those amendments were understood only to apply to acts of Congress, not the states, and it would not be until well after the passage of the Fourteenth Amendment (since the Privileges and Immunities Clause, which should have immediately applied all those provisions to the states, was instead ignored in the
Slaughter-House Cases) that such state laws, including anti-blasphemy laws, were struck down.