Church and state

"Congress shall make no law respecting an establishment of religion,
or prohibiting the free exercise thereof."

http://www.law.cornell.edu/supct/index.html

1925, Gitlow v. People [New York]
Criminal anarchy is the doctrine that organized government should be
overthrown by force or violence, or by assassination of the executive
head or of any of the executive officials of government, or by any
unlawful means. The advocacy of such doctrine either by word of
mouth or writing is a felony.
The legislature has authority to forbid the advocacy of a doctrine
designed and intended to overthrow the government without waiting
until there is a present and imminent danger of the success of the
plan advocated.

1940, Cantwell v. Connecticut
Newton Cantwell and his two sons, Jesse and Russell, members of a
group known as Jehovah's Witnesses were going door-to-door in a
thickly populated neighborhood where about ninety percent of the
residents are Roman Catholics. They were soliciting money,
services, subscriptions or any valuable thing for their religious
cause. "unless such cause shall have been approved by the
secretary of the public welfare council." The state contends the
statute imposes no previous restraint upon the dissemination of
religious views or teaching, but merely safeguards against the
perpetration of frauds under the cloak of religion.
The statute is to be read as requiring the officer to issue a
certificate unless the cause in question is clearly not a religious
one, and that, if he violates his duty, his action will be corrected
by a court.
The conviction of Jesse Cantwell on the fifth count must be set
aside. The State of Connecticut has an obvious interest in the
preservation and protection of peace and good order within her
borders.
The offense known as breach of the peace embraces a great variety
of conduct destroying or menacing public order and tranquility.
It includes not only violent acts, but acts and words likely to
produce violence in others. A State may not unduly suppress free
communication of views, religious or other, under the guise of
conserving desirable conditions.

1947, Everson v. Board of Education
A township board of education, acting pursuant to this statute,
authorized reimbursement to parents of money expended by them
for the bus transportation of their children on regular busses
operated by the public transportation system. Part of this
money was for the payment of transportation of some children
in the community to Catholic parochial schools. These church
schools give their students, in addition to secular education,
regular religious instruction conforming to the religious tenets
and modes of worship of the Catholic Faith. The superintendent of
these schools is a Catholic priest.
The First Amendment has erected a wall between church and state.
That wall must be kept high and impregnable. We could not approve
the slightest breach. New Jersey has not breached it here.