The anthem (a musical term derived from antiphon) was originally an English development of the motet. It is a choral setting of a sacred or moral text usually sung during a service.
Whilst a four-part unaccompanied form is known from the mid-16th century, by about 1600 there began variations in which added solo voices and instrumental (usually organ) accompaniment appeared. The anthem became a formal part of the Anglican service and was acknowledged in the Book of Common Prayer of 1662. By then it was being written in a more dramatic style and strings began to appear. It reached full potential with Handel’s Coronation and Chandos Anthems in the first half of the 18th century. (Handel’s first Coronation Anthem, “Zadoc the Priest” is one of the most-loved choral pieces of all time.)
Like all forms of English music the anthem languished somewhat after Handel but enjoyed a revival in Victorian times culminating in the fine works of Stanford, then moved beyond the church in the 20th century with arrangements by Ralph Vaughan Williams, Arnold Bax and Benjamin Britten that are as much at home in the concert hall as in places of worship.
The anthem arrived in America during the 18th century and, by 1800, more works by American-born composers were being used than imported anthems, especially in New England. The form was enriched from input by German immigrants and still thrives in American churches.