بسم الله الرحمن الرحيم
Shaykh Muhammad ibn Umar Bazmool explains the following statement of Shaykh Muhammad ibn Abdul Wahhab (as found in the article: Tawheed With Respect To Worship):
"In addition you're aware that this is tawheed, that which is more binding upon you than prayer and fasting. Allah will forgive whoever comes with it on the day of resurrection and will not forgive whoever is ignorant of it despite him being a devout worshiper."
The shaykh says, "In this (statement) there's a pointing towards the issue of excusing an individual due to ignorance. Hence the author's intent -may Allah bestow mercy upon him- is that whoever has the ability to learn, and acquire understanding of tawheed yet he is lenient (in that regard), or shuns (learning) it, or is lazy and as a result he falls into polytheism and whatever else that contradicts tawheed from directing acts of worship to other than Allah, then there's no excuse for him due to ignorance even if he be the most devout in worship from the people.
So whoever is ignorant concerning tawheed and his condition is like what was previously mentioned then there is no excuse for him.
Whoever says: "I say that there is no diety in truth except Allah," yet he goes around circling the grave (like what is performed at the Kabah as worship to Allah) then we say, you are ignorant with regards to the meaning there's no deity in truth except Allah and your Islam is not affirmed fundamentally, you are not excused due to ignorance. What is implied by you saying I'm a Muslim and there is no deity in truth except Allah and Muhammad is the Messenger of Allah, yet you sacrifice to the inhabitant of the grave, you vow to him, and you go around circling his grave, what is the meaning of this? You're not excused for your ignorance. For this reason the author said, "and (He) will not forgive whoever is ignorant of it..."
The (specific) situation related to the lack of excuse due to ignorance here is for whomever had the ability to seek knowledge and understanding of tawheed, however he shunned it and turned away, or he was negligent and lazy (concerning the learning of it). And this is the issue that pertains to excusing one due to ignorance. The Scholars have established (the fact) that the fundamental affairs of the religion that which are prerequisites of the religion, such as the actualization of the two testimonies by way of that which was mentioned previously (in the book from which this is extracted), is that no one is excused for being ignorant of it due to it being the religion. It is Islam.
Consequently no one is excused for being ignorant in this regard if he has the ability to understand the truth and seek knowledge of it, yet he persists in falling into polytheism and other actions that contradict tawheed.
Source: شرح توحيد العبادة
Translated by Najeeb Al Anjelesi