They are enclosed in their own fat - The meaning here is, that they were prosperous, and that they were consequently self-confident and proud, and were regardless of others. The phrase occurs several times as descriptive of the wicked in a state of prosperity, and as, therefore, insensible to the rights, the wants, and the sufferings of others. Compare Deuteronomy 32:15, “But Jeshurun waxed fat and kicked: thou art waxed fat, thou art grown thick, thou art covered with fatness; then he forsook God which made him,” etc. Job 15:27, “because he covereth his face with his fatness, and maketh collops of fat on his flanks.” Psalms 73:7, “their eyes stand out with fatness.” Psalms 119:70, “their heart is as fat as grease.”
With their mouth they speak proudly - Haughtily; in an arrogant tone; as a consequence of their prosperity.