From: Middle English prophesien, from Anglo-French prophecier, from Old French, from prophecie
Date: 14th century
transitive verb (i.e. requiring a direct object)
1 to utter by or as if by divine inspiration
2 to predict with assurance or on the basis of mystic knowledge
intransitive verb (i.e. cannot take a direct object)
1 to speak as if divinely inspired
2 to give instruction in religious matters: preach
3 to make a prediction
Hexham's Concise Dictionary of Religion
To prophesy is to conduct the act of revelation, giving an inspired message from God or the Gods. Usually a prophecy is associated with foretelling the future, but it can also include messages of inspiration or admonishment that reveal the will of God towards a particular people or even an individual.
Grammar plays an important role in determining the use of the term "to prophesy." In its transitive form, the act of prophesying implies that the message originates from a deity ("The minister prophesied rewards for the faithful and punishment for the wicked."). In its intransitive form, prophesying derives from the human speaker ("The minister prophesied in the Sunday morning sermon.") In its intransitive form, therefore, anyone is capable of prophesying, to teach, to predict, or simply to make observations.
In this broader view, any oration in a religious venue can be viewed as an act of prophesying. Ordained clergy, who have generally received extensive instruction in religious matters and gone through a discernment process to prepare them for ordination, might be expected to regularly prophesy as part of the practice of homiletics (delivering sermons aimed at the spiritual needs, capacities, and conditions of a congregation). When viewed as a profession, prophesying might be considered an act expected of ministers to offer insight, inspiration, and instruction through preaching.
Atheist Definition: Prophesying is the act of speaking or writing to make observations, to inspire, or to teach others regarding religious matters.