The fool's hostility to the knowledge of God leads to a mind that no longer serves its original purpose, that of discovering the works of God and co-laboring with Him, giving Him glory. The depraved mind of a fool instead serves a different purpose, the advancement of an idol god largely defined by unrestrained lusts. This episode unpacks the usurpation of the mind in service of idolatry. Paul notes that unbelieving Gentiles "walk, in the futility of their mind, being darkened in their understanding, excluded from the life of God because of the ignorance that is in them, because of the hardness of their heart." (Ephesians 4:18) Working backwards through the quote, Gentile hostility to the knowledge of God, based on "hardness of heart" makes them ignorant and disqualifies them as participants in the life of God. Without the knowledge of God (deliberately suppressed), the mind can't possibly serve its original purpose. The understanding is darkened, the mind itself a futile faculty, cut off from the life of God. The consequent "depraved mind" exists to service the idol identity grounded in the big three ("the lusts of the flesh, the lusts of the eyes, and the boastful pride of life"--1 John 2:16) "Sensuality for the practice of every kind of impurity with greediness" (Ephesians 4:19) is relatively easy, for the conscience, acting on the inner law of God, has been largely deactivated. The Holy Spirit has given the fool over to a depraved mind that is "callous" and resistant to correction. The litany of character defects in Romans 1:29-31 is predictable: "full of envy, murder, strife, deceit, malice, gossips, slanderers, haters of God, insolent, arrogant, boastful, inventors of evil, disobedient to parents, without understanding, untrustworthy, unloving, and unmerciful."
