Rational or irrational?
Thomas Bayes was a Presbyterian minister.
Bayes’s first publication was a theological work, entitled Divine Benevolence ([Bayes], 1731). Since no author appears on the title page of the book, or anywhere else, it is sometimes considered to be of doubtful authorship. For example, the National Union Catalog of the United States ascribes authorship to Joshua Bayes. However, Thomas Bayes was the author of this work. Bayes’s friend, Richard Price refers to the book in his own work A Review of the Principal Questions in Morals (Price, 1948, p. 248) and says that it was written by Thomas Bayes. In Divine Benevolence Bayes was trying to answer the question of the motivating source of God’s actions in the world.
The essay dealt with how to handle the problem of evil in the world. It is also believed that Bayes was an Arian.
That is from a D.R. Bellhouse paper (pdf), with a relevant pointer from Asher Meir.