Ma'at was important for many reasons in Egyptian society. She plays a key role in most versions of the creation myth and is occasionally called "Mother of the Earth".
She was responsible for the balance of the universe and was usually said to be the cause of any fortune (good or otherwise). The concept of Ma’at (order, harmony, balance) was used to explain many important natural occurrences, like the changing of the seasons and the balance between the Nile and the desert.
Egyptian life was based on order and balance in both society and the natural world. Because of this, Ma’at was extremely important and well respected in Egyptian society, and Ma’at was thought to govern nearly every aspect of Egyptian life.
Though Ma'at was rarely worshipped in temples, it was important to try and please her on a regular basis. She was the fulcrum on which a spirit was weighed and judged in the afterlife and was therefore constantly present in an Egyptian's every day life. Much like the Christian "Ten Commandments", ancient Egyptians were expected to uphold the "42 Principles of Ma'at" (eg. do not steal)
The justice system was there to uphold the values of Ma’at, though she was not directly related to law. People involved in the justice system were called Priests of Ma’at, even the Pharaoh himself.
Ma’at and the Pharaoh were very closely linked. Pharaohs called themselves the Beloved of Ma’at. They had to rule in a way that kept order and harmony. If they didn’t, it was believed that chaos would occur.