After Moshe receives instructions for confronting Paroh, he returns to his father-in-law Yitro and asks for permission to head back to Egypt, which is granted (4:18). Why did Moshe feel the need to get the green light from Yitro when he obtained specific instructions from G-d to head back to Egypt?

Rabbi Chaim Shmulevitz submits that because Yitro opened up his home when Moshe was a fugitive and treated him with dignity, Moshe could not leave without asking permission. This example of derech eretz (literally the way of the land/proper conduct) is the basis upon which the Torah was given. While the Torah consists of 613 mitzvot (commandments/laws) or building blocks, proper conduct (morals and ethics) is the mortar that keeps the blocks together, which is a concept that Moshe highlights for us with his honorable actions.