Christian views of Islam shifted from chastisement to Antichrist as Muslim power grew.

Evidence

The difference between Sophronios’s view of the Arab invaders as a divine chastisement and the Apocalypse of Pseudo-Methodius’s portrayal of them as forerunners of the Antichrist is one of degree, not nature; they are given a more prominent role in God’s plan to correspond with their enormous political, military, and spiritual successes. — John V. Tolan, Saracens, 335