Being excused for not knowing the principles and rulings of Islam
one is excused for his/her unawareness of the articles of faith and fundamentals of Islam, if the message of the Qur'an and the Sunnah of His Prophet (peace be upon him) is conveyed to him/her. Allah states,
...this Qur’ân has been revealed to me that I may therewith warn you and whomsoever it may reach.
He also says,
This (Qur’an) is a Message for mankind (and a clear proof against them), in order that they may be warned thereby
Similar Ayahs (Qur'anic verses) convey the same meaning. As for the subsidiary matters whose rulings may seem ambiguous, ignorance is declared as an excuse until the proof is set, as there are many Hadiths related in this regard.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.