Ah, you may say, "But there are only 12 chromatic notes. How original can a person's music really get?"
Fortunately there are many other devices that provide variety. RHYTHM, HARMONY, TEMPO, INSTRUMENTAL COLORS, CULTURAL FLAVORS are a few of these devices. Over the years, composers have constantly been developing new STYLE characteristics. Because many composers within a certain time period tended to gravitate to using similar characteristics and even outright copied each other's techniques, musicologists have divided these into stylistic time periods. Some major ones reflected many of the artistic and architectural modes of their day such as Baroque, Classical, Romantic, Modern, 20th Century, and so on. That is not even mentioning the many and varied Popular and Folk styles that have developed over the centuries.
While it is generally assumed that Church Music is slower to adapt and change to the most current musical styles, there may be good reason for that. Often composers get so excited about writing in new and different ways that they forget who they are writing for. (Older people, for example, do not like fast or drastic changes of any kind.) So, stylistic changes in Sacred Music come about more slowly.
Variety is great in Sacred Music, provided that it supports the spiritual message. The musical writing should support the message of the text and not pull undue focus to itself. Bearing testimony of the Savior and His teachings and inviting the Spirit are the most important elements. The musical compositional style should suit these parameters.
And yet, using the same melodic motives, or rhythmic patterns in the accompaniment, or the same chord progressions over and over can get old pretty quickly. There are so many options to choose from and styles to be influenced by that composers should have no trouble finding inspiration to create great Sacred Music.
Here's a little Christmas piece influenced highly by music of many great composers. Enjoy "Shepherds Shake Off Your Drowsy Sleep" for SATB, Baritone Soloist and Piano.