@joshbeaudette
"I completely agree with everything you stated other than the part about states being allowed to have official religions. That would give preference to that particular religion over the others, which is why there is a separation between any specific church and "state". "
The First Amendment to the US Constitution explicitly forbids the U.S. federal government from enacting any law respecting a religious establishment, and thus forbids either designating an official church for the United States, or interfering with State and local official churches — which were common when the First Amendment was enacted. It did not prevent state governments from establishing official churches. Connecticut continued to do so until it replaced its colonial Charter with the Connecticut Constitution of 1818; Massachusetts retained an establishment of religion in general until 1833. (The Massachusetts system required every man to belong to some church, and pay taxes towards it; while it was formally neutral between denominations, in practice the indifferent would be counted as belonging to the majority denomination, and in some cases religious minorities had trouble being recognized at all.)
The Fourteenth Amendment to the US Constitution, ratified in 1868, makes no mention of religious establishment, but forbids the states to "abridge the privileges or immunities" of U.S. citizens, or to "deprive any person of life, liberty, or property, without due process of law". In the 1947 case of Everson v. Board of Education, the United States Supreme Court held that this later provision incorporates the First Amendment's Establishment Clause as applying to the States, and thereby prohibits state and local religious establishments. The exact boundaries of this prohibition are still disputed, and are a frequent source of cases before the US Supreme Court — especially as the Court must now balance, on a state (similar, but not equivalent to province) level, the First Amendment prohibitions on government establishment of official religions with the First Amendment prohibitions on government interference with the free exercise of religion.
All current U.S. state constitutions include guarantees of religious liberty parallel to the First Amendment, but eight (Arkansas, Maryland, Massachusetts, North Carolina, Pennsylvania, South Carolina, Tennessee, and Texas) also contain clauses that prohibit atheists from holding public office. However, these clauses have been held by the United States Supreme Court to be unenforceable in the 1961 case of Torcaso v. Watkins, where the court ruled unanimously that such clauses constituted a religious test incompatible with the religious test prohibition in Article 6 Section 3 of the United States Constitution.
In short, the states themselves have chosen to mirror the US Constitution, but the US Constitution does not prohibit the establishment of an official state religion as it would never have been ratified by a number of states at the time had it done so.