Their heart is as fat as grease,.... Or tallow, a lump of it, fat or grease congealed. That is, the heart of the above proud persons, who abounded in riches, were glutted with the things of this world; had more than heart could wish, and so became proud and haughty: or their hearts were gross, sottish, senseless, and stupid, as persons fat at heart are; or as creatures over fat, which have little or no feeling: so these had no knowledge of the law of God, no sense of their duty, no remorse of conscience for sin; their hearts were hardened, and they past feeling, and given up to a reprobate mind; see Isa 6:9; The Targum is, "the imagination of their heart is become gross as fat:'' the Septuagint is, "curdled like milk"; that is, hardened, as Suidas (s) interprets it; but I delight in thy law; after the inward man; as the apostle did, Rom 7:22; as fulfilled in Christ; as in his hands, as King and Lawgiver; as written upon his own heart; and so yielding a ready and cheerful obedience to it; he delighted in reading the law, in meditating on it, and in observing it. (s) In voce