The Bible uses a large variety of metaphors, imagery, similes, types, parables, allegories, and analogies as teaching tools. They are used either to hide or cloud a meaning from outsiders, or sometimes to make them clear—so that God's people understand either way. Here, in Exodus 4:21, Israel is shown as a cohesive body—as a single, human son. In other places, Israel is portrayed as a virginal woman, married to God, and in yet other places, as a harlot who is still legally married but who, in reality, has left the marriage and pursued lovers.
In like manner, the church is typified as a body (of which Christ is the Head) and the firstborn of God. In another analogy, the church is portrayed as the firstfruits—not a body, but an assembly of individuals harvested as a crop. In another place, it is pictured as a loaf of bread that has leaven in it. The New Testament contains many other symbols for the church.
John W. Ritenbaugh
New Covenant Priesthood (Part 1)
God's warning to the Egyptians that He would kill their firstborn was part of the plan from the beginning. It was not, as The Ten Commandments movie would have one believe, a last minute decision to which God resorted when all the other plagues failed to achieve His desired effect. In His mercy, God repeats His warning to Pharaoh, giving him plenty of opportunity to repent: "[A]ll the firstborn in the land of Egypt shall die, from the firstborn of Pharaoh who sits on his throne, even to the firstborn of the maidservant who is behind the handmill, and all the firstborn of the beasts" (Exodus 11:5).
The Law of the Firstborn
Other Forerunner Commentary entries containing Exodus 4:22: