Final answer:
The official list of New Testament books that form the canon as we know it today was established in 1442 during the Renaissance, after a long period of discussion and debate within the Christian Church. Prior to this, various texts, including the Gospels and other writings, were used by Christian communities, but there was no universally accepted list.
Step-by-step explanation:
Lists of the New Testament books that are nearly identical to the official list appeared in 1442. Before this time, the four Gospels - Matthew, Mark, Luke, and John - as well as other books of the New Testament were already in circulation and used by Christian communities. However, the definitive 'canon' of scripture, which determined the exact writings considered authoritative and inspired for the Church, was established during the Renaissance.
The process of canonization involved extensive debate and discussion among religious scholars and leaders. It took centuries for the Church to officially settle on which texts would be included. This included well-known codices such as the Vulgate translated by Jerome, which was a significant Latin version of the Bible and was influential for over a millennium in the western Church.
Additionally, illustrated and illuminated texts like those found in the beautiful Book of Kells helped to convey and interpret the New Testament narratives. The codex format was particularly useful for traveling priests and for the spreading of the Christian faith. The official recognition of the New Testament canon at the Council of Florence in 1442 established the books that would collectively constitute the definitive New Testament.