In Exodus chapter eleven, verse five, the Lord instructs Moses to go to Pharoah and tell him one more plague will come to Egypt. God indicates to His servant that afterward, the King of Egypt will let the Israelites go.
God, Himself, would bring the final judgment upon the Egyptians: the firstborn son of every family would die. This deadly plague would be a terrible blow to the Egyptians because the firstborn carried on the Father’s hopes and ambitions. God’s judgment was His atonement because of the Egyptians’ wickedness. Their cruelty to the Hebrews and the drowning of the male babies were persecution of God’s “firstborn.” The Egyptians were reaping what they had sown.
The tenth and final plague was the death of the firstborn: It included both people and animals of the Israelites and the Egyptians. The plague consisted of the firstborn killed. To avoid punishment, the people would kill a sacrificial lamb (sheep or goat) and paint the door posts with the blood. When the Lord passed through the land, He would not destroy the firstborn that had shown their trust in His provision of salvation.
By the destroying angel inflicting disease upon them, however, it was sudden and immediate death, which was universal, reaching all the firstborn in the families of the Egyptians in all parts of the kingdoms. The responsibility of the King of Egypt is to take care of the city, the people, and their supplies. After the sixth plague, some of Pharoah’s servants were concerned about what was happening in Egypt with the plagues. Pharoah did listen but did not want to give in to the request of Moses and the God of Israel. He did not want to change the system that was in place for almost four hundred years, with the Israelites being under the authority of him being King of Egypt and in his control.