Commentaries:
Most commentators feel that God struck Moses with a life-threatening illness by which He was going to kill, to slay. It came to Moses, undoubtedly during prayer or meditation, that the problem was his resisting God in the circumcision of his son.
There is an interesting sidelight here. From the information provided, the son had not been circumcised because Moses conceded to Zipporah that the son would not be circumcised. What God was teaching Moses is that, as the head of the house, he was responsible to see that God's rules, orders, policies, and directions were followed.
Once he passed the test, Moses was convinced of something else: He knew that Zipporah could not go with him to Egypt. Therefore, he sent her back, and he went on alone. At least his life was spared because he followed through in doing what he should have done.
John W. Ritenbaugh
Conviction, Moses, and Us
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 One)
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).
Staff
The Law of the Firstborn
