Islam is Christianity's greatest rival. This is true historically as well as in our own time. For the Reformers, Islam posed a greater threat to the church than did Roman Catholicism. Luther thought of both the Pope and the Turk as antichrist. Calvin maintained that Muhammad was one of the two horns of antichrist. By Calvin's time Islam had been a force to reckon with for almost a thousand years, and had wreaked havoc on the church. Calvin wrote that ...the sect of Mohammad was like a raging overflow, which in its violence tore away about half of the church.
In the 1645 Westminster Assembly's Directory for Public Worship ministers were instructed to lead their congregations in prayer for the deliverance of the distressed churches abroad from the tyranny of the antichristian faction, and from the cruel oppressions and blasphemies of the Turk (Islam).
Today's reformers do not seem aware that Islam has plans to tear away the other half of the church. I suspect that prayers for churches distressed by the oppressions and blasphemies of Islam are relatively rare on most Sunday mornings. Protestants continue to keep one eye suspiciously peeled toward Rome while the other eye that should be watching Mecca remains closed.
However, Calvin and the Reformers did not simply foresee the rise of Islam, they predicted its fall. There was no doubt in the mind of Calvin that Christianity would triumph over Islam. Even more significantly, Calvin believed that Muslims would be converted in great numbers. Through the undeserved goodness of God, Calvin wrote, the Assyrians and Egyptians shall be admitted to fellowship with the chosen People of God...Calvin based this belief from reading Isaiah 19:23-25. In that day there will be a highway from Egypt to Assyria. The Assyrians will go to Egypt and the Egyptians to Assyria. The Egyptians and Assyrians will worship together. In that day Israel will be the third, along with Egypt and Assyria, a blessing on the earth. The LORD Almighty will bless them, saying, "Blessed be Egypt my people, Assyria my handiwork, and Israel my inheritance."
Indeed, Calvin saw the first fruits of God's goodness when Muslims were requesting baptism after making professions of faith.