Final answer:
Arthur is crowned King during the religious festival of Pentecost in 'Le Morte d'Arthur', emphasizing the divine endorsement of his rule and the theme of renewal.
Step-by-step explanation:
In Le Morte d'Arthur, Arthur is finally crowned King during the religious festival of Pentecost. This is significant as Pentecost is a major Christian festival that commemorates the descent of the Holy Spirit upon the apostles and other followers of Jesus Christ, as described in the Acts of the Apostles. Arthur's coronation during this time highlights his divine right to rule and signals a new beginning in the monarchy, echoing themes of renewal and rebirth that are associated with the Pentecost celebration.