Some time ago I listed the thoughts of Luther and Calvin on Islam. This post continues that summation.
Calvin observes that although Muslims were thought to be far away, they could quickly arrive in Protestant Europe:
When we preach at the present day about the Turk, all think that it is a fable, because they think that he is still at a great distance from us. But we see how quickly he overtook those who were at a greater distance and more powerful. So great is the insensibility of men that they cannot be aroused, unless they are chastised and made to feel the blows. Let the inhabitants of Babylon, therefore, be a warning to us, to dread, before it is too late, the threatenings which the prophets utter, that the same thing may not happen to us as happens to those wicked men, who, relying on their prosperous condition, are so terrified when the hand of God attacks and strikes them, that they can no longer stand, but sink down bewildered. (on Is 13.5)
He cautions against being happy to see Muslim armies defeat other nations in Christendom:
Something of this kind happened, not long ago, to many nations who had taken great delight in seeing their enemies vanquished by the Turk: they found that such victories were destructive and mournful to themselves; for, after the defeat of those whom they wished to see destroyed, the road to themselves was likewise thrown open, and they also were defeated. (on Is 14.31)
He also blames France in his day for collaborating with the Muslim Turks and in doing so endangering the rest of Christendom:
The case was similar to that of the Turks at this day, were they to pass over to these parts and exercise their authority; for it might be asked the French kings and their counsellors, “Whose fault it is that the Turks come to us so easily? It is because ye have prepared for them the way by sea, because ye have bribed them, and your ports have been opened to them; and yet they have wilfully exercised the greatest cruelty towards your subjects. All these things have proceeded from yourselves; ye are therefore the authors of all these evils.” (on Jer 13.21)