Complex sentence: He wrote to the people that the existing order and practices at the time were diametrically opposed to the teachings of the Qur'an and the Sunnah and challenged the scholars to be critical of the old order and the Tijaniyya doctrine.
Split into simpler sentences: He wrote to the people that the existing order and practices at the time were diametrically opposed to the teachings of the Qur'an and the Sunnah. He challenged the scholars to question the old order and encouraged them to be critical of the Tijaniyya doctrine.