Around 1968, or earlier, is when Boyd began his interest in L Ron Hubbard‘s Church of Scientology, which would make him one of the first Hollywood stars to follow this religion. Boyd had always expressed an interest in esoteric religions. In an interview in August 1969 with the Detroit Free Press, he said that Scientology helped him through the filming of Slaves, and that it is “a process used to make you capable of learning. Scientology is nothing. It means only what you want it to. It is not a church you go to to pray, but a church that you go to to learn. It is no good unless you apply it. It is the application”. Boyd apparently had been elevated to a Scientology Status of OC 6, a position beneath that of Clear. Boyd would actually go on to star and narrate a Scientology recruiting film called Freedom in 1970. A copy of this film can be found at the Library of Congress, but it is not available online via any Scientology resource, which may indicate a falling out Boyd had with the Church using his name for recruiting purposes. There is no documentation of his later involvement with this religion.
Interesting Stephen Boyd interview below concerning his first encounter with Scientology in New York.