Addressing the Muslims the Quran says:
And thus have We made you a just and balanced community so that you serve as witnesses (for Divine Truth) over mankind and that the Prophet be a witness over you – (2:142).
According to this verse shahadah is the purpose for which the Muslim Ummah has been raised;  it is the Ummah’s raison d’être. What is shahadah? It begins with the assertion of what is aptly described by the same word, shahadah:
‘I stand witness that none is deserving of worship and obedience except Allah alone without any partner; and I stand witness that Muhammad is his slave and messenger.’
This assertion implies commitment on behalf of the reciter of shahadah to the fact that he will follow the commandments of Allah in every sphere of his or her life and that these commandments are embodied in the message conveyed to mankind by Muhammad (SAW) in the form of the Quran and his life-example. This message was the same, in its essentials, with all the messengers of Allah raised in all ages and at all places, and was finally perfected through Muhammad (SAW).
Shahadah begins with verbal assertion accompanied, of course, by a deep conviction. This has to be evidenced by the deeds of the person who renders shahadah. This – conviction, verbal declaration and conduct appropriate to it – is individual shahadah. But the mission of shahadah is incomplete unless it is realized in the collective life of the believers as well. That is why the Quranic verse quoted above says that evidence has to be given just as the Prophet (SAW) did it. He stood as a witness for the world to the Divine truth not only in his individual life but by creating an ideal society organized on the lines of this Truth. For this he struggled throughout his holy life and offered incomparable sacrifices including the sacrifices of his nearest relations and dearest companions who rendered shahadah by offering the final sacrifice.            

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