and touched Moses' feet with it.
you and your descendants after you for the generations to come.
This is my covenant with you and your descendants after you,
and it will be the sign of the covenant between me and you.
or bought with money from a foreigner --
will be cut off from his people;
God had not made Abraham do the same. However, God gave Abraham the sign of circumcision as a way for Abraham to express the same type of idea: "May God cut off me and my descendants if I am not faithful in keeping the LORD alone as my God." Abraham no doubt would have been careful to convey this information to his descendants.
Moses knew about this covenant sign. He probably had also spoken of the significance of these matters to Zipporah his wife as well. How do I know this? Well, when Moses is in the midst of nearly being killed by the LORD, Zipporah seems to know exactly what to do to turn away the LORD's wrath from her husband.
The LORD had chosen Moses to lead His people out of Egypt. Moses' allegiance had to be to God first, not Zipporah or anyone else. It is reassuring that God did not show favoritism. Leaders sometimes do not follow the rules which they expect others to obey. This would not be permitted with Moses. God held himself to the same strict standard: If Pharaoh was to be called into account for his rebellious ways, then so was Moses.
Therefore, God's actions toward Moses had not been freaky at all. He had done exactly what He had said He would do to those who refused to follow His covenant instructions. By ignoring the covenant sign of circumcision (for whatever reason), Moses had put both himself and his two sons at risk of being cut off from the people of Israel.