Where? The Constitution says nothing about a speration of Church and Stae, but it details how government cannot silence or impede religion.
Enforce what?
Practice, speak about, gather in any number and talk about, or print any form of literature about a religion, that cannot be oppressed or silenced BY anyone or anything by the protection of the constitution?
Psst, hint, it's the very first "right" mentioned and guaranteed.
James Madison
The civil Government, though bereft of everything like an associated hierarchy, possesses the requisite stability, and performs its functions with complete success, whilst the number, the industry, and the morality of the priesthood, and the devotion of the people, have been manifestly increased by the total separation of the church from the State (Letter to Robert Walsh, Mar. 2, 1819).
Strongly guarded as is the separation between religion and & Gov't in the Constitution of the United States the danger of encroachment by Ecclesiastical Bodies, may be illustrated by precedents already furnished in their short history (Detached Memoranda, circa 1820).
Every new and successful example, therefore, of a perfect separation between the ecclesiastical and civil matters, is of importance; and I have no doubt that every new example will succeed, as every past one has done, in showing that religion and Government will both exist in greater purity the less they are mixed together (Letter to Edward Livingston, July 10, 1822).
I must admit moreover that it may not be easy, in every possible case, to trace the line of separation between the rights of religion and the civil authority with such distinctness as to avoid collisions and doubts on unessential points. The tendency to a usurpation on one side or the other or to a corrupting coalition or alliance between them will be best guarded against by entire abstinence of the government from interference in any way whatever, beyond the necessity of preserving public order and protecting each sect against trespasses on its legal rights by others. (Letter Rev. Jasper Adams, Spring 1832).
To the Baptist Churches on Neal's Greek on Black Creek, North Carolina I have received, fellow-citizens, your address, approving my objection to the Bill containing a grant of public land to the Baptist Church at Salem Meeting House, Mississippi Territory. Having always regarded the practical distinction between Religion and Civil Government as essential to the purity of both, and as guaranteed by the Constitution of the United States, I could not have otherwise discharged my duty on the occasion which presented itself (Letter to Baptist Churches in North Carolina, June 3, 1811).
Thomas Jefferson
The clergy, by getting themselves established by law and ingrafted into the machine of government, have been a very formidable engine against the civil and religious rights of man (Letter to J. Moor, 1800).
The clergy...believe that any portion of power confided to me [as President] will be exerted in opposition to their schemes. And they believe rightly: for I have sworn upon the altar of God, eternal hostility against every form of tyranny over the mind of man. But this is all they have to fear from me: and enough, too, in their opinion (Letter to Benjamin Rush, 1800).
History, I believe, furnishes no example of a priest-ridden people maintaining a free civil government. This marks the lowest grade of ignorance of which their civil as well as religious leaders will always avail themselves for their own purposes (Letter to von Humboldt, 1813).
In every country and in every age, the priest has been hostile to liberty. He is always in alliance with the despot, abetting his abuses in return for protection to his own (Letter to H. Spafford, 1814).
Mr. President
To messers Nehemiah Dodge, Ephraim Robbins, & Stephen S. Nelson a committee of the Danbury Baptist association in the state of Connecticut.
Gentlemen
The affectionate sentiments of esteem & approbation which you are so good as to express towards me, on behalf of the Danbury Baptist association, give me the highest satisfaction. my duties dictate a faithful & zealous pursuit of the interests of my constituents, and in proportion as they are persuaded of my fidelity to those duties, the discharge of them becomes more & more pleasing.
Believing with you that religion is a matter which lies solely between man & his god, that he owes account to none other for his faith or his worship, that the legitimate powers of government reach actions only, and not opinions, I contemplate with sovereign reverence that act of the whole American people which declared that their legislature should make no law respecting an establishment of religion, or prohibiting the free exercise thereof, thus building a wall of separation between church and state. [Congress thus inhibited from acts respecting religion, and the Executive authorised only to execute their acts, I have refrained from presenting even occasional performances of devotion presented indeed legally where an Executive is the legal head of a national church, but subject here, as religious exercises only to the voluntary regulations and discipline of each respective sect.] Adhering to this expression of the supreme will of the nation in behalf of the rights of conscience, I shall see with sincere satisfaction the progress of those sentiments which tend to restore to man all his natural rights, convinced he has no natural right in opposition to his social duties.
I reciprocate your kind prayers for the protection and blessing of the common Father and creator of man, and tender you for yourselves and your religious association, assurances of my high respect & esteem.
(signed) Thomas Jefferson
Jan.1.1802.