Erasmus of Rotterdam was a "correspondent" of Martin Luther, and this quote came out around the time of Luther's publishing the "95 Theses," attacking the sale of indulgences and other practices of the Catholic Church.
The context was a "choosing sides" issue. As every boy learns on the playground, "you don't want to be the odd man out in a three cornered fight."
Although Catholicism and Protestantism were technically both "Christian" religions, they regarded each other with such mutual suspicion and dislike that the "pagan" Turkish Moslems seemed preferably to each than the other was.
The strongest defenders of the Catholic faith were the Hapsburgs, and the countries most likely to be friendly toward the Turks were the anti-Hapsburgs. This included Catholic (!) France of Francis I, Erasmus of Rotterdam, the Netherlands, that would soon turn Protestant and rebel against the Hapsburgs, and (much later) Frederick II (the Great) of Prussia, who said, "[If] honest people wish to populate our land, be they Turks or Pagans, we will build mosques and churches for them.