Tertullian - The Prescription against Heretics

The character of the times in which we live is such as to call forth from us even this admonition, that we ought not to be astonished at the heresies (which abound) neither ought their existence to surprise us, for it was foretold that they should come to pass; nor the fact that they subvert the faith of some, for their final cause is, by affording a trial to faith, to give it also the opportunity of being “approved.”  
 
-Tertullian