11. Those tares of changing the canonical penalty to the penalty of purgatory were evidently sown while the bishops slept (Mt 13:25).
This section of Matthew is the parable where Jesus teaches that a farmer sows good seed and then in the night while the farmer slept, an enemy comes and sows weeds (tares) among his good seeds and both grow up together. This is Luther’s reference to the teaching of the tares among the good seeds as something like how the penalty of purgatory was taught in the church while the bishops slept. So it had become an accepted teaching along with the rest of the teachings of the church.
Luther’s point here is that if the leaders of the church had been paying attention to the things that were being taught in the church, they could have caught this false teaching before it became a common understanding. He is also saying that it is something that has so engrained itself into the core of the church’s teachings that it may now be hard to pull out. Therefore even Luther believed in purgatory even though he found no support for that in Scripture.
Again you can see Luther has a respect for the canons of the church even though he feels that the bishops and the priests have forgotten to follow them. Also Luther has used the Matthew reference for a purpose that it was not meant to teach. He quotes it as someone who is completely familiar with the text of scripture and likes the picture these words bring.
Dear Father in heaven, please keep me from error as I live for you, that I may not ignore the words of scripture and instead study them as my path to a life lived for you. In Christ, Amen.