Walther nails it. It is preposterous how the Anabaptists and those today can turn a precious gift that Christ has given us, into a work. The blog post is worth the read.
I liked this quote specifically:
Every heresy that has sprung up was caused by the heretic’s inability to believe that man becomes righteous in the sight of God, and is saved, by grace alone. That is the real rock of offense against which all heretics, all false teachers, dash their head. But there is no escape from this dilemma: either believe this truth or see what will become of you.