Answer:
Shahadah is the is the foundation and essence of Islam.
" I bear witness that there is no god except Allah, who is One, Who has no partners, and I bear witness that Muhammad is His servant and apostle. "
Without accepting it a person cannot enter the fold of Islam. It is a declaration of faith in Oneness of God and his Uniqueness, and that Muhammad is only His servant and apostle.
It is the first step to being a Muslim and it differentiates a believer from a a non-believer. It is also important to consider that Muhammad is a human and nothing beyond that, he is the messenger of God, sent to the world to show the righteous path and separate good from bad. When we accept this we take the responsibility to follow the law and system shown by him.
Not only does a person have to say it out verbally, but he has to believe in what he said and act accordingly . That includes avoiding any act that harms other people or animals.
Declaration of Shahadah does not only mean that you believe in the one God but you have to take your responsibility as a human being to make this world a better place.
