This depends upon one's legal philosophy.
"Living Document" types will argue that the 1st Amendment means whatever we as a nation want it to mean.
"Struct Constructionists" will argue that we should examine only what it says.
But "Originalists" will consider writings of the founders when interpreting the 1st Amendment.
Ref...
History of the Separation of Church and State in America
Some Excerpted portions...
....in an 1802
letter to the Danbury Baptists, Thomas Jefferson made clear that
the purpose of the First Amendment was to establish a "wall of separation"
between Church and State in order to protect individuals' right of conscience:
"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, & 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 & State. 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."
In addition to all of this, there was a reference to Christianity in
Thomas
Jefferson's first draft of the
Declaration of Independence, however the
reference was not positive. In Jefferson's rough draft he wrote:
"he has waged cruel war against human nature itself, violating it's most sacred rights of life & liberty in the persons of a distant people who never offended him, captivating & carrying them into slavery in another hemisphere, or to incur miserable death in their transportation thither. this piratical warfare, the opprobrium [disgrace] of infidel powers, is the warfare of the Christian king of Great Britain. determined to keep open a market where Men should be bought & sold, he has prostituted his negative for suppressing every legislative attempt to prohibit or to restrain this execrable commerce: and that this assemblage of horrors might want no fact of distinguished die, he is now exciting those very people to rise in arms among us, and to purchase that liberty of which he has deprived them, & murdering the people upon whom he also obtruded them; thus paying off former crimes committed against the liberties of one people, with crimes which he urges them to commit against the lives of another."