When does “al-amīn” add rhetorical value in “jāʾa al-rasūlu al-amīnu”?

Ījāz, Iṭnāb and Musāwāt: Standards of Expression and Their Distinctions

• When the adjective is known and contributes nothing
• When the messenger’s reliability is relevant
• When the adjective only repeats a prior predicate
• When it omits an essential part of the message