Monotheism is the belief in one God, and ethical monotheism in the belief that our ethics or morality comes from this God.
It is important, as this is the prodominant view of Christians, Muslims and Jews, and as such influenced the behaviour of a big part of human population. It also means that people's morality can be influenced by religious leaders, who claim they know what pleases this God.
The main difference between the two is that ancient Egyptians worshiped many gods and goddess meaning they were polytheistic. The Israelites worshiped one god meaning they were monotheistic.
