and Muhammad (peace be upon him) is His Prophet
From the time of making Shahadah, the person is treated and respected like a Muslim by all Muslims, even if he/she was previously an enemy of Islam. There are many examples of this in the history of the Prophet (peace be upon him).
The bond of faith is much stronger than the bond of blood. When a person becomes a Muslim they enter the community of Muslims, regardless of their race or background. A feeling of love and harmony abides between people who sincerely seek to practice Islam according to the Qu'ran and Sunnah. Such people are in a race to do good and be those with whom Allah is pleased.
The significance of the Shahadah is further highlighted, when we ponder on the fact that we repeat it every time we pray. How many of us, really think about it during prayer? It becomes a usual thing and maybe sometimes we say the words without contemplating their meaning.
When we say there is no god worthy of worship except Allah, it means that we disdain obedience and servitude to anyone or anything except Allah. It means that we fear no one and nothing except Allah: that our greatest feeling of love and gratitude are kept for Allah, because we know that He is the real Provider of all we have. It means that we do not seek the pleasure or acceptance of anyone or anything except Allah. This means that the Muslim becomes strong and independent. The ridicule, scorn, sneers and insults of people bear no importance. The Muslim remains calm and secure in times of panic because they know that there is no help except from Allah. In times of grief and distress, the Muslim remains steadfast and courageous, knowing that calamity can only occur with the permission of Allah and that He, in His Mercy has promised not to bear a sincere soul, with more than it can bear.
When we say that Muhammad is the Prophet of Allah, we acknowledge his right to be respected, obeyed and revered. We follow in his footsteps, knowing that he was the best of creation and hope to achieve Paradise and be close to him and the other prophets, Inshaa Allah.
Truly the Shahadah is not a empty phrase, it is not just a few words spoken but is coupled with sincerity of intention and determination to struggle, strive and sacrifice along the straight path.