Because religious belief, or non-belief, is such an important part of every person's life, freedom of religion affects every individual. Religious institutions that use government power in support of themselves and force their views on persons of other faiths, or of no faith, undermine all our civil rights. Moreover, state support of an established religion tends to make the clergy unresponsive to their own people, and leads to corruption within religion itself. Erecting the "wall of separation between church and state," therefore, is absolutely essential in a free society.
"[When] the [Virginia] bill for establishing religious freedom... was finally passed,... a singular proposition proved that its protection of opinion was meant to be universal. Where the preamble declares that coercion is a departure from the plan of the holy author of our religion, an amendment was proposed, by inserting the word "Jesus Christ," so that it should read "a departure from the plan of Jesus Christ, the holy author of our religion." The insertion was rejected by a great majority, in proof that they meant to comprehend within the mantle of its protection the Jew and the Gentile, the Christian and Mahometan, the Hindu and infidel of every denomination." --Thomas Jefferson: Autobiography, 1821. ME 1:67
"No man shall be compelled to frequent or support any religious worship, place, or ministry whatsoever, nor shall be enforced, restrained, molested, or burthened in his body or goods, nor... otherwise suffer on account of his religious opinions or belief... All men shall be free to profess and by argument to maintain their opinions in matters of religion, and... the same shall in no wise diminish, enlarge, or affect their civil capacities." --Thomas Jefferson: Statute for Religious Freedom, 1779. ME 2:302, Papers 2:546