Exodus 4:21 - 23

"The Lord said to Moses, 'When you return to Egypt, see that you perform before Pharaoh all the wonders I have given you the power to do. But I will harden his heart so that he will not let the people go. Then say to Pharaoh, "This is what the Lord says: Israel is my firstborn son, and I told you, 'Let my son go, so he may worship me.' But you refused to let him go; so I will kill your firstborn son."'" NIV translation

God gave Moses his final instructions which were basically a warning to complete all of the signs that were given to him. 

We see that they were to be performed for the Pharaoh and not as some kind of show. (Today, there are many who want to put the power of God on display like a kind of circus show but that IS NOT God's desire.)

We also see that the Lord is going to harden Pharaoh's heart for His purposes and the result will be the plague on the firstborn sons.

Exodus 4:24 - 26

"At a lodging place on the way, the Lord met Moses and was about to kill him. But Zipporah took a flint knife , cut off her son's foreskin and touched Moses' feet with it. 'Surely you are a bridegroom of blood to me,' she said. So the Lord let him alone. (At that time she said 'bridegroom of blood,' referring to circumcision.)" NIV translation

Along the way to Egypt, the wrath of God was about to break out against Moses. He had not circumcised his son as required under the Abrahamic covenant. This was the mark of the people of God and he was responsible for his son being circumcised. His wife stepped in and recognized what had to be done. In so doing, she saved the life of Moses. Today, many people try to minimize the role of a Godly woman/wife. As we see with Moses, it is crucial for a man of God to have a Godly wife. If Zipporah had not known about the things of God, Moses would have died.