Final answer:
John was sent to bear witness of the light of Christ, which in Christian theology represents divine truth and grace, as seen in both scripture and religious art.
Step-by-step explanation:
The light John was sent to bear witness of refers to the light of Christ. In Christian theology and scripture, Christ is frequently referred to as the light of the world, a manifestation of divine truth and grace. This concept is illustrated through various narratives and artworks, such as the Transfiguration of Jesus where he shines with divine light, and through representations in religious structures like churches, where light plays an essential role in the spiritual experience and is seen as a pathway to contemplation of God. In scripture, particularly the Gospel of John and other New Testament writings, John the Baptist plays a crucial role in testifying to the divine light represented by Jesus Christ, preparing the way for his ministry.