Why did the Founding Fathers feel that the 'free exercise' and establishment clauses of the First Amendment were so important?

Britain had established the Church of England as its official religion. People of other beliefs were frequently persecuted for their beliefs. Many of these groups escaped Britain to settle in the New World to escape this persecution. Therefore, throughout the colonies, there were many different religions represented with each being dominant in one or more regions. The founding fathers also recognized the strength of immigration. Remember the French and some Germans who helped during the Revolution. These were predominantly Catholic and Protestant countries. By codifying the free exercise of religion and not permitting any future establishment of a state religion, they allowed for freedom of a type frequently not allowed and prevented (at least to some degree) future official persecution of others.