Complex sentence: Most diptychs of the period illustrated one of a small range of religious scenes, including numerous depictions of the Virgin and Child Smith (2004), 178 which reflect the Virgin's contemporary popularity as a subject of devotion.
Split into simpler sentences: Most diptychs of the period illustrated a small range of religious scenes. There are numerous depictions of the Virgin and Child, Smith (2004), 178 reflecting the Virgin's contemporary popularity as a subject of devotion.