כי כבד פה וכבד לשון אנכי. The very fact that Moses mentioned both these deficiencies of his separately is a clear indication that he had difficulty in formulating certain words which are articulated with the teeth. The consonants he had difficulty with were זשרצס, and when he referred to difficulty as כבד פה, he had in mind the letters דתל'ט.

בני בכורי ישראל. Moses is to tell Pharaoh in G’d’s name that if He had delivered the Israelites under his control in order to discipline them somewhat this was not because He, their G’d, had rejected them. We know this from Moses telling the people in Deuteronomy 8,8 that any discomfort they had ever been subjected to in their journey was due to the discipline administered by a loving father to miscreant children. The father does not enjoy punishing his children but it is necessary in order for them to learn that misconduct carries a price. Pharaoh had greatly exceeded the authority he had to be G’d’s agent in educating the Israelites. As a fitting retribution G’d would kill Pharaoh’s own firstborn during the last of the plagues. When G’d referred to the Israelites as בני בכורי ישראל , this was a complimentary description of them, as for instance the line בני א-ל חי, “Children of the living G’d” in Hoseah 2,1. Similarly, Mount Sinai, a sanctified mountain is also referred to as הר ה', “G’d’s mountain,” in Numbers 10,33. Similarly, the Holy Temple, the holiest of structures, is known as “the House of the Lord” in Isaiah 56,7 The precise wording there is “for My House is called a House of Prayer.”

ויהי בדרך במלון ויפגשהו ה' ויבקש המיתו; Moses was not present at the inn. The Torah had written prior to this that Moses had taken his wife and his sons and let them ride on the donkey. (verse 20) The meaning of the verse is that he sent his family ahead of him. Immediately afterwards we are told that Moses himself returned to Egypt. If the Torah reports sequentially, Moses could not have been at the inn at the time Tzipporah had this encounter. ויבקש המיתו, the person under threat of death was the boy, seeing that the angel had assumed the form of a serpent about to swallow the little boy. This serpent then spit out the boy and began to devour him from the opposite end, swallowing up to the part where the circumcision was to be performed. At that point, ותקח צפורה צור, Tzipporah understood what the problem was, i.e. that they were being punished for being tardy in performing the boy’s circumcision so that she herself performed it with a sharp flint.