Why MOTHER's Right is Greater than Father's?

Someone asked the Messenger of Allah (saw), "Who has the greater right over children, the mother or the father?"

The Messenger of Allah (saw) answered, "The mother's right is greater than the father's." He was asked three times, and each time the answer was the same. The fourth time, Messenger of Allah (saw) said, "The father's right is next."

"Why do you give the mother three rights to the father's one?"

The Messenger of Allah (saw) replied, "Your mother carried you for nine months in her womb, than gave you birth. After that she gave up her sleep for your sleep, suckled you, carried you in her arms, and cleaned you. For years she cooked for you, fed you, and served you food. She did your laundry. When you were forty, fifty, sixty, she still followed your progress with interest. Your father sowed you in your mother's womb, provided your food, and made sure you had clothes to wear. Can this be compared with your mother's role?" 

And We have enjoined man in respect of his parents - his mother bears him with faintings upon faintings and his weaning takes two years - saying: Be grateful to Me and to both your parents; to Me is the eventual coming. And if they contend with you that you should associate with Me what you have no knowledge of, do not obey them, and keep company with them in this world kindly, and follow the way of him who turns to Me, then to Me is your return, then will I inform you of what you did. Noble Qur'an (31:14-15)

The questioner went on, "Well, I wonder if I could ever repay my mother for all the help and service, however much I might do for her?

The Messenger of Allah (saw) replied, "you could not repay so much as one night's due!

"But suppose I carry my mother on my back for years, clean up after her, cook for her, and feed her. Suppose I attend to those same services as long as she may live?" "There will still be this difference between you: your mother looked out for you to live, while you are waiting for her to die."

Resources: Islamic Website 

Moral ; Mother is like an angel that guard us start from her womb (rahem) until we were able to live independently.. and still be surveying on us until the end of her life..