Which word would best describe an 'epistle' in a historical context?

In a historical context, the term 'epistle' is best described as a formal letter. This designation stems from its usage in literature and religious texts, where epistles often served as important communications between individuals of note or within communities, conveying significant messages or teachings.

The formal nature of epistles distinguishes them from other forms of written communication. They were typically composed in a structured manner, addressing recipients with respect and often containing thoughtful deliberations on various subjects. This contrasts with other options, such as a brief message, which implies a lack of depth or seriousness, or a casual message, which conveys an informal tone. A journal entry, on the other hand, usually reflects personal thoughts or experiences and lacks the formal, communicative intent associated with an epistle. Thus, the word ‘formal letter’ aptly encapsulates the essence and historical function of an epistle.