Tithing
Tithing (or Tithe) is defined by Merriam-Webster's Dictionary as to pay or give a tenth part of especially for the support of the church.
Speech Relevance
In 'Encroaching Control' Reagan talks about the income tax system:
Both the old and new testament describe tithing as the economic basis of our Judaic and Christian religions. We are told that we give the Lord a tenth and we are told that if the Lord prospers us ten times as much, we give ten times as much. But when you start computing Caesar's share under our present tax system you'll find that the man of average income, if he has prospered ten times as much, his personal income tax goes up 53 times as much.