Song meaning

The first verse ("In 325, the Council devised a set of sacred testaments (...)") is about the "First Council of Nicaea". The First Council of Nicaea was a council of Christian bishops convened in Nicaea in Bithynia (present-day İznik in Turkey) by the Roman Emperor Constantine I in A.D. 325. The Council was the first effort to attain consensus in the church through an assembly representing all of Christendom.

The second verse ("In old Tennessee, the last century (...)")  is about "The Scopes Trial". The Scopes Trial was an American legal case in 1925 in which high school biology teacher John Scopes was accused of violating the state's Butler Act which made it unlawful to teach evolution.