This one of those times when if you read the story very carefully you may find more clues. For example; “And Moses took his wife and his [b]son[u]s[/u][/b], and set them upon an ass, and he returned to the land of Egypt: and Moses took the rod of God in his hand.” (Ex 4:20 KJVS)…so there is no doubt that there were 3 men in this party, Moses, Gershom (Ex 2:21-22) and another son. We deduce this from the fact that the scripture refers to ‘sons’ ie at least two.
However later in the account we read…“Then Zipporah took a sharp stone, and cut off the foreskin of her [b]son[/b], and cast it at his feet, and said, Surely a bloody husband art thou to me.” (Ex 4:25 KJVS)…which implies that of the 3 males present only one was circumcised by Zipporah at this time. (still with me?)
So what possible scenario can we derive from this? Here is my suggestion. Moses would have been circumcised in Egypt as a child. What of Gershom? Jethro, Gershom's maternal grandfather, was a Midianite and although they had some knowledge of God there were vital missing elements from their pattern of faith. As far as the record shows Jethro was never brought into covenant with God. He had lots of information but a distant relationship with God. (there’s a sober warning!)
Circumcision was the sign of the Abrahamic covenant and Midian although descended from Abraham (Gen 25:1-2) but by Keturah. Midian was not a child of promise but of the flesh; he was never party to the covenant promises which Abraham received. He had the right father but the wrong mother. We can compare the Galatians comments on another child of Abraham’s who had the right father but the wrong mother. (Gal 4:22-23) The Midianites became of the traditional enemies of the people of Israel. Again we can remind ourselves of the Galatians truth; “But as then he that was born after the flesh persecuted him that was born after the Spirit, even so it is now.” (Gal 4:29 KJVS) The Midianites were the people that God raised Gideon to deal with. (Judg 6:1-2)
We also find that during the Exodus period the Midianites were in alliance with the Moabites. “And the elders of Moab and the elders of Midian departed with the rewards of divination in their hand; and they came unto Balaam, and spake unto him the words of Balak.”(Num 22:7 KJVS) It is illuminating to trace the history of the Midianites and their opposition to God and his plans. )Gen 25:2,4; 36:35; 37:28,36; Ex 2:15-16; 3:1; 4:19; 18:1; Num 10:29; 22:4,7; 25:6,14-15,17-18; 31:2-3,7-9; Josh 13:21; Judg 6:1-3,6-7,11,13-14,16,33; 7:1-2,7-8,12-15,23-8:1; 8:3,5,12,22,26,28; 9:17; 1Kings 11:18; 1Chr 1:32-33,46; Psa 83:9; Is 9:4; 10:26; 60:6; Hab 3:7)The Midianites are religious compromisers who will ultimately frustrate the purposes of God.
Here is my scenario… Moses first child is born and pretty little bird Zipporah says ‘you’re not with your own people now there is no need to circumcise Gershom’. But Moses refuses to hear her reasonings and Gershom is circumcised. When the next child comes along a few years later Moses recollections of his early days are somewhat dimmed and perhaps it doesn’t seem such a big issue any more. This time when Zipporah sings her song (Zipporah means Little Bird) Moses relents and the second son is not circumcised. So there is a male in Moses family who has not been circumcised and it looks as if Moses has got away with it.
But on the journey to Egypt the past comes back with a vengeance. Circumcision speaks of the ‘crucifixion of the flesh’ and a refusal to trust in natural energy. Moses will be God’s spokesman but the power that delivers Israel will be God’s alone. Moses is made to see this plainly. In the caravanserai God holds Moses in a death grip and Zipporah somehow knows what the issue is. It’s that circumcision thing again! She circumcises her youngest son (just the one) and throws the foreskin at Moses’ feet with a cry of exasperation at her husbands ‘bloody religion’. “Then Zipporah took a sharp stone, and cut off the foreskin of her son, and cast it at his feet, and said, Surely a bloody husband art thou to me. So he let him go: then she said, A bloody husband thou art, because of the circumcision.” (Ex 4:25-26 KJVS) Zipporah has gone through the ritual but at heart she is still a Midianite. She has finally obeyed but not without a final protest.
God cannot and will not use ‘uncircumcised/uncrucified' natural strength to effect his deliverances and Moses, [i][b]and we too[/b][/i], must learn that lesson lest we die.
Most of the above is ‘speculation’. It is my ‘best fit’ hypothesis.