"The next day he went out and saw two Hebrews fighting. He asked the one in the wrong, 'Why are you hitting your fellow Hebrew?' the man said, 'Who made you ruler and judge over us? Are you thinking of killing me as you killed the Egyptian?' Then Moses was afraid and thought, 'What I did must have become known.' When Pharaoh heard of this, he tried to kill Moses, but Moses fled from Pharaoh and went to live in Midian, where he sat down by a well." NIV translation
The next day, Moses tried to do the right thing and break up a fight between two of his fellow Hebrews. In doing so, he found out that the murder that he committed was not a secret and, in fact, Pharaoh found out and tried to kill him. This is a reminder to us that, even though we may think that our sins are hidden, they are known. It also reminds us that Moses was not chosen to deliver the people based on his own goodness as he was known to be a murderer. In the same way, we as Christians are not chosen to serve God based on our goodness but on the goodness of God.
Here, Midian refers to a place and the place is named after a son of Abraham. After the birth of Isaac and Jacob, he took another wife and had children with her; one of those boys was named Midian. Because of the fact that they were children of Abraham, these people would have known about the one true God but they also worshipped other gods.
This particular priest had seven daughters and no sons. Although we may not understand it, this would have been a source of shame in not having a son to carry on the family name. His daughters tended his flock but were pushed around by the other shepherds who were probably men. Moses defended them and was able to water their flock.
"When the girls returned to Reuel their father, he asked them, 'Why have you returned so early today?' They answered, 'An Egyptian rescued us from the shepherds. He even drew water for us and watered the flock.' 'And where is he?' he asked his daughters. 'Why did you leave him? Invite him to have something to eat.'" NIV translation
Normally, the girls would have had to wait while the male shepherds watered their flocks before they could do their job. Seeing that his daughters returned much earlier than normal, their father asked what had happened and they told him about Moses. We are also reminded of the fact that Moses had been trained as an Egyptian and was even mistaken for one by the girls. He looked, talked, and acted like an Egyptian due to his forty years of training in the royal courts.