observance vs theology

observance

noun
  • A rule governing a religious order, especially in the Roman Catholic church. 

  • The practice of complying with a law, custom, command or rule. 

  • That which is to be observed. 

  • Observation or the act of watching. 

  • The custom of celebrating a holiday or similar occasion. 

  • Reverence; homage. 

theology

noun
  • A particular belief within a religion. 

  • Synonym of religious studies 

  • Subjective marginal details. 

  • An organized method of interpreting spiritual works and beliefs into practical form. 

  • The study of God, a god, or gods; and of the truthfulness of religion in general. 

How often have the words observance and theology occurred in a corpus of books? (source: Google Ngram Viewer )