Pope Francis cites Scripture, but the description is familiar to anyone who has experience with the Ignatian discipline of discernment of spirits. The path of sin for a believer is far different from that of someone blind to virtue. Perhaps this is especially relevant during these days of scandal and cover-up and pleas of innocence in the face of disturbing evidence.
165. Spiritual corruption is worse than the fall of a sinner, for it is a comfortable and self-satisfied form of blindness. Everything then appears acceptable: deception, slander, egotism and other subtle forms of self-centeredness, for “even Satan disguises himself as an angel of light” (2 Corinthians 11:14). So Solomon ended his days, whereas David, who sinned greatly, was able to make up for disgrace. Jesus warned us against this self-deception that easily leads to corruption. He spoke of a person freed from the devil who, convinced that his life was now in order, ended up being possessed by seven other evil spirits (cf. Luke 11:24-26). Another biblical text puts it bluntly: “The dog turns back to his own vomit” (2 Peter 2:22; cf. Proverbs 26:11).
You can check the full document Gaudete et Exsultate on the Vatican website.