Here's my explanation for the Hatan Damim story with an assist from Ady Manory
Moshe is reluctant to go on his Impossible Mission. He offers every excuse and tries every escape. Finally, he agrees to go, but his heart isn't in it. He takes Tzipora along, knowing she and the boys will slow him down (Rashbam) He lies to his father-in-law about his reason for leaving. And he dallies at a lodge.
In the section immediately before the lodge story, God tells Moshe
And you shall say to Pharaoh, 'So said the Lord, "My firstborn son is Israel. So I say to you, 'Send out My son so that he will worship Me, but if you refuse to send him out, behold, I am going to slay your firstborn son."
Moshe's reluctance to carry out the mission can only result from one thing: He doesn't believe that God will stand with him. He thinks he will be on his own , and he knows he can't do it alone. So what does God do to correct this error? He endangers Moshe's first born son. This causes Moshe to realize that God will do anything for Israel, his firstborn son, and that his mission will not be allowed to fail (Raavad) But during the demonstration, Tziporah panicked and worried that her son would die uncircumcised, so she performed the bris herself and tossed the bloody foreskin at Moshe saying, "You did this! You are a bridegroom of blood. Your delay has put us all in danger".
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