Walz v. Tax Commission:
"There is a line between what a State may do in encouraging "religious" activities, Zorach v. Clauson, 343 U. S. 306, and what a State may not do by using its resources to promote "religious" activities, McCollum v. Board of Education, 333 U. S. 203, or bestowing benefits because of them. Yet that line may not always be clear. Closing public schools on Sunday is in the former category; subsidizing churches, in my view, is in the latter."
The course of constitutional neutrality in this area cannot be an absolutely straight line; rigidity could well defeat the basic purpose of these provisions, which is to insure that no religion be sponsored or favored, none commanded, and none inhibited. The general principle deducible from the First Amendment and all that has been said by the Court is this: that we will not tolerate either governmentally established religion or governmental interference with religion.