A khatib delivers the khutbah, the sermon that precedes Friday congregational prayer, jumu'ah, and is also given on other significant occasions such as the two annual Eid festivals; the khutbah traditionally follows a structured form, opening with praise of God and blessings on the Prophet Muhammad, addressing a substantive religious, ethical or, at times, communal or current-events theme, and closing with further prayers, a structure that has remained recognizably consistent across regions and centuries even as the specific content addressed has naturally varied with the concerns of a given time and place. In most mosques the role of khatib is combined with that of imam, the same individual delivering the Friday sermon and then leading the prayer that follows it, though larger institutions sometimes designate the two functions separately, particularly where a mosque wishes to draw on a respected outside speaker's specific expertise for the sermon while its regular imam continues to lead the prayer itself.
Friday sermons have historically also served, in various Muslim societies and periods, as a significant channel of public communication beyond purely religious instruction, including conveying rulers' or governments' messages to the public in some historical and contemporary contexts, a use of the khutbah's platform that has made control over who may serve as khatib, and what may be said from the pulpit, a point of political as well as religious significance in a number of Muslim-majority states.