The spirit of the message of Islam can be summed up and shown in this phrase: La ilaha illa'llah."- There is no god but Allah. It means that, apart from the One and Only Allah, nothing must be worshipped. This is the great, fruitful, abundant secret of the tree of Islam. For if we compare Islam to a tree, and its ideology to the seed or the root, we must realise that the health and fruitfulness of the tree is connected to the health of the roots. And then we see how strong, how steadfast and steely the basis of the ideology of Islam is, as revealed in this one phrase.
source : http://www.maaref-foundation.com