Why is it difficult to make a definitive ruling regarding the Basmala in prayer if the religion is clear? Is it always possible to make a definitive ruling between different opinions? Are there still texts whose abrogation or other matters have not been conclusively decided?

Religion is clear in its fundamentals, but some of its issues are subject to ijtihad (definition) (independent reasoning) and permissible disagreement among scholars, allowing for competition in seeking knowledge and attaining reward. The mujtahid (one who performs ijtihad) is rewarded even if he errs, and the common person imitates whoever he trusts. Disagreement can be a mercy and a breadth, as stated by Sheikh Al-Islam Ibn Taymiyyah and Omar ibn Abd al-Aziz. In matters of ijtihad, one does not denounce with the hand, nor is anyone compelled to follow a specific opinion; rather, they are discussed with scholarly arguments. The disagreement regarding whether the Basmala is a verse of Al-Fatiha or not is of this type. The scholar acts according to what he deems most likely to be correct, and the common person imitates whoever he trusts. The truth is never hidden from all scholars of the Ummah; their consensus is a conclusive proof, and they will never agree upon error.