Mr. Andy Underhile at: http://andycontramundum.blogspot.com/2010/03/holy-heresy-part-1.html
Holy Heresy - Part 1
At first blush, it seems like a strange statement to say that heresy is “necessary” to the condition of the true Church. But history demonstrates the truth of this assertion. The great ante-Nicene African theologian, Tertullian, wrote, “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’.” 1 Even St. Paul warned that heresies must occur. He said, “For there must be also heresies among you, that they which are approved may be made manifest among you.” 2
Perhaps at this point we should define heresy. In the earliest uses it meant primarily the work of schismatic or divisive teachers within in the Church. But by the writing of Peter’s second epistle, heresy had come to mean the false teachings of these schismatic or divisive teachers. This is the meaning which has persisted to the present day. Peter calls their teaching,”damnable heresies.” 3
But even in the Old Testament, God warned Israel that false teachers would arise and that the whole point was to test Israel’s faithfulness to God’s Law. Moses wrote, “If there arise among you a prophet, or a dreamer of dreams, and giveth thee a sign or a wonder, and the sign or the wonder come to pass, whereof he spake unto thee, saying, Let us go after other gods, which thou hast not known, and let us serve them; thou shalt not hearken unto the words of that prophet, or that dreamer of dreams: for the Lord your God proveth you, to know whether ye love the Lord your God with all your heart and with all your soul.” 4 This means that just because a leader is attractive this is no guarantee that he is led by God. New ideas from inspiring people may sound good, but we must judge them by whether or not they are consistent with God’s Word.
Throughout the history of the Church, heresies have forced us to formulate more clearly what we mean to say by the terminology we employ. In the first four centuries of the Church, the heresies of Marcion, Arius, Paul of Samosata, Nestorius, Eutyches, Sabellius and Pelagius drew forth from the early Fathers the great Creeds of Nicaea, Constantinople and the definition of Chalcedon. During the Reformation era, the Remostrants prompted the synod of Dort. This is perhaps one of the greatest services of heresy for the true Church: it forces us to think clearly. We are required by the exigencies of the situations to declare the whole counsel of God not in an “uncertain sound.” 5 One thinks of the great Councils of Nicaea, Orange and Dordt as examples of this process. When error encroaches upon the Church, the Lord raises up an Athanasius, a Prosper, a Luther, a Calvin or a Voetius to help the Church more clearly define what she means by the terms she uses.