The conversion of an inventor of false doctrine has never yet been heard of; for a sin such as this is too great, because it blasphemes God’s Word and sins against the Holy Ghost. This is why God lets inventors of false doctrine become hardened. Accordingly, the word of Is. 6:9 is fulfilled: With seeing eyes you shall not see, and with hearing ears you shall not hear; for the heart of this people is hardened.
Christ converted no high priest; but their disciples were converted, men such as Nicodemus, Joseph, Paul, and the like. The prophets of old converted no false prophet. Neither could Paul convert any false prophet; but he gave the direction: After a person has been admonished twice or three times, he is to be avoided and let go, as a perverted one (Titus 3:10). Thus even the holy doctors have never yet converted a master of heresy, not because none of them ever sufficiently combated their error and refuted it with the truth but because their heart was obsessed with their own notion. They fared like a man who looks through a colored glass. Put before such a man whatever color than that of the glass. The fault is not that the right color is not put before him but that his glass is colored differently, as the word of Is. 6:9 puts it: You will see, he says, and yet you will not see it. This means: It will be put before your eyes sufficiently and clearly, so that you may see it; and others will actually see it, but you will not see it. What else could it mean? This is the reason why one cannot convert such people (says John 12:40). The truth presented to them does not do it. God must remove the colored glass. This is something we cannot do.
What Luther Says, p. 644
Compiled By Ewald M. Plass