A reader asks why Protestant pile of dung theology is a re-hash of Arianism. It would have been more precise to say that it is a re-hash of Adoptionism. Whoops. Blog posts are written quickly. 

First I should explain what I mean by ‘Protestant pile of dung theologies.’ This is a reference to Luther’s idea that because of original sin we are totally depraved and are worthless in God’s eyes. However, because of the death of Christ God looks on us and does not see our sin and depravity, but Christ’s righteousness. Luther likened this to a pile of dung that is covered by snow.

This is more technically (but less colorfully) called ‘imputed righteousness.’ Catholics do not believe this. We believe that through faith and baptism, and the continued sacramental life of grace, Christ’s righteousness is infused into us, not imputed. In other words, it doesn’t just cover us, making us superficially and outwardly good in God’s eyes. Instead, God’s grace really does get into us and transforms us from the inside out. It gets down deep to the very foundations of our being and re-makes us into the image of Christ.
Adoptionism was the Christological heresy that Jesus Christ was not truly and completely divine, but that his divinity was something he ‘adopted’. One such teaching said he became divine at his baptism. This is unsatisfactory because it suggests that he was a sinful person who simply had divinity imputed to him at some stage. This parallels the Protestant pile of dung theologies because they also suggest that Christ’s righteousness is not something that is deep within us as a transforming power, but something that is simply imputed to us.
However, there is a parallel to Arianism as well. Arius taught that Jesus Christ was not truly one with the Father. Inasmuch as ‘pile of dung theologies’ deny that we can experience theosis and be truly transformed into the likeness of Christ, they echo Arianism’s denial of the full integration of God and Man in Christ Jesus.