Your Questions was
‘How Important is it to come out of the Sectarian Islam first, to understand TRUE ISLAM?’
Following verses of Qur’an answer your question
56:77 That this Qur’an is a Noble Monograph.
56:78 In a well-guarded Book. [As conveyed to you]
56:79 This is a Book that none but the pure of mind can grasp.
[Those who approach the Qur’an with minds contaminated with preconceived notions and extrinsic material, will never understand it. Mutahharoon = Those who rid their minds of blind following and false dogmas. (2:222). It is a common insult to say that men cannot touch it without wudhu (ablution) and women cannot touch it during menstruation. Why would God place hurdles in the way of approaching His guidance?]
2:163 Remember, your God is One God. There is no god but He, the Beneficent, the Merciful.
Unless you have the courage to say LA (to false gods of Sectarian Islam ) you cannot reach Allah .