By the statement: "Knowledge of Islam has to be substantiated by evidence", the author means that
it is obligatory on a Mukallaf (person meeting the conditions to be held legally accountable for their actions) to know Islam and its pillars from its principal sources, namely, the Qur'an and Sunnah. Thus, a Muslim has to learn Tawhid (belief in the Oneness of Allah/monotheism) and whatever may detract from its perfection or contradict it. A Muslim also has to learn Salah (Prayer), its fundamentals, obligatory and recommendable acts, from the Qur'an as well as from the sayings, actions and approvals of the Prophet (peace be upon him). The same applies to other pillars and rituals of Islam.By his statement: "Allah sent us a Messenger; Whoever obeys him will enter Paradise and whoever disobeys him will enter Hellfire", the author means that Allah (Glorified and Exalted be He) sent Muhammad (peace be upon him) with Tawhid and the rest of the laws of Islam. Whoever responds to him, embraces Allah's Religion, obeys Allah's Commands, and avoids His Prohibitions will enter Paradise. On the other hand, whoever rejects faith, disobeys the Messenger (peace be upon him), and refuses to embrace Allah's Religion will enter Hellfire. (Part No. 2; Page No. 26) Allah (Exalted be He) says:
He who obeys the Messenger (Muhammad صلى الله عليه وسلم), has indeed obeyed Allâh, but he who turns away, then we have not sent you (O Muhammad صلى الله عليه وسلم) as a watcher over them.
Moreover, the Prophet (peace be upon him) is authentically reported to have said:
'My entire Ummah (nation based on one creed) will enter Paradise except those who refuse.' They (the Companions)said, 'O Messenger of Allah, who will refuse?' He (peace be upon him) said, 'Anyone who obeys me will enter Paradise, and anyone who disobeys me has refused.'
May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family and Companions.