Exodus 9:3, commentary and pictures

Moses was to warn that if Pharaoh kept refusing to release Israel, the hand of the Lord would fall in judgment upon Egypt's cattle in the field — upon the horses, asses, camels, oxen, and sheep — in a very grievous murrain, a still more terrible visitation than those before it. Its time was announced beforehand and it came as predicted, so it could not be dismissed as happening by chance. The murrain struck and destroyed the Egyptian cattle it visited, including beasts of burden and sacred animals.

The cattle of the Israelites were distinctly exempted as Moses had declared, so that not one of them died or was afflicted. That exemption extended to all that belonged to Israel, while the plague destroyed the Egyptian cattle except those belonging to the Israelites. By killing sacred bulls, rams, heifers, goats, and other venerated animals, the plague struck at Egypt's worship of animals. It showed that its animal gods could not protect themselves or their worshipers and that Jehovah alone is supreme.

The plague was meant to demonstrate to the Egyptians that the whole earth is under the command of the God of the Hebrews and that thunder, hail, and storm obey His voice. Pharaoh verified the distinction by inquiry, sending messengers to the homes of the Israelites who found they had entirely escaped. Yet he hardened his heart and remained obstinate and refused to release Israel, encouraged in persistency by the priests and magicians, until proud Pharaoh would be humbled to confess his sin and the righteousness of the Lord.