Select the most appropriate one-word substitution for the given group of words.

One who studies God and religion

theologian

The most appropriate one-word substitution for "one who studies God and religion" is theologian.

The other words in the options, theist, theorist, and atheist, do not mean the same thing.

• Theist is a person who believes in God or gods.
• Theorist is a person who develops theories about a particular subject.
• Atheist is a person who does not believe in God or gods.

A theologian is a scholar who studies religion, especially the nature of God and religious beliefs. They typically have a deep understanding of different religious traditions and are able to critically analyze religious texts and ideas.