oration by a member of the clergy
A sermon is an oration or lecture by a preacher (who is usually a member of clergy). Sermons address a scriptural, theological, or moral topic, usually expounding on a type of belief, law, or behavior within both past and present contexts. Elements of the sermon often include exposition, exhortation, and practical application. The act of delivering a sermon is called preaching.
In Christian churches, a sermon is usually preached in a place of worship, either from an elevated architectural feature, known as a pulpit or an ambo, or from behind a lectern. The word sermon comes from a Middle English word which was derived from Old French, which in turn originates from the Latin word sermō meaning "discourse". A sermonette is a short sermon (usually associated with television broadcasting, as stations would present a sermonette before signing off for the night).
The Bible contains many speeches without interlocution, which some take to be sermons: Moses in Deuteronomy 1–33; Jesus' sermon on the mount in Matthew 5–7 (though the gospel writers do not specifically call it a sermon; the popular descriptor for Christ's speech there came much later); and Peter after Pentecost in Acts 2:14–40 (though this speech was delivered to nonbelievers and as such is not quite parallel to the popular definition of a sermon).
In modern language, the word sermon is used in secular terms, pejoratively, to describe a lengthy or tedious speech delivered with great passion, by any person, to an uninterested audience.
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A Sermon on Education, Wherein Some Account Is Given of the Academy, Established in the City of Philadelphia
sermon by Richard Peters and published by Benjamin Franklin