Although our existence is from Allah (Glory and Greatness be to Him), it is our parents who are the means of giving us life. We are an offshoot of their existence and a fruit of the garden of their unparalleled affection, training, love and sentiments. When the forgetful human being grows up to become big and strong and comes to acquire a certain credibility (in life), he forgets the period wherein he was weak and lacking in strength. He disregards the exhaustive efforts of his parents; what ingratitude could be worse than this?
Humanity and ethics demand that we safeguard these two jewels (our mother and father) - by exhibiting goodness towards them while they are alive, and by means of charity and goodly remembrance after their death.
Our lives are an extension of our parent's lives while our children's lives are a continuation of ours. Our good behavior towards our parents and our exhibition of kindness towards them shall cause our children to grow up as grateful and righteous individuals. They shall behave with us just as we have behaved with our own parents.
Just as it is beyond our means to fulfill the rights of Allah (Glory and Greatness be to Him) and to thank Him for all His bounties in their entirety, similarly we can never thank our parents sufficiently for their efforts. The only thing that we can do is to acknowledge our inability and submit ourselves, in humility and reverence, before these two angels. However, comprehension of their status in the eyes of Allah (Glory and Greatness be to Him) paves the way to fulfill some of their numerous rights.