Their heart is as fat as grease; the sense is either,
1. They are stupid, and insensible, and past feeling, not affected either with the terrors or comforts of God's word. So the like phrase is used Isaiah 6:10, compared with 1 Thessalonians 12:40. Or,
2. They prosper exceedingly, and are even glutted with the wealth and comforts of this life. But I delight in thy law; but I do not envy them their jollity, and I have as much delight in God's law as they have in worldly things.