Al-Qurtubee in his tafseer, he talks about people who say when they read the Qur`aan 'this comes to my mind', or 'my heart tells me this'. He concludes that whoever reads the Quraan and says, "ask your heart" or "my heart tells me," and so forth, they are speaking about Allaah without knowledge ('ilm), which, as we will talk about, is one of the greatest sins that we could commit, and that they are actually from zanaadiqa, those who have nothing to do with Islaam, and he said they should be killed as apostates (murtadeen).
When you go to the Qur`aan and you read a verse from the Qur`aan and you explain that verse without having the proper knowledge, without following the proper methodology, you might be and only Allaah (swt) knows, actually following your own hawaa (desires), you might be following an inspiration from the Shaytaan, you might be following dhann (conjecture), which Allaah (swt) speaks about in many places in the Qur`aan, or it might actually be some kind of inspirataion from Allaah (swt), but most likely it is not the last case. And why is it not the last case? Because as we will talk about it later, you did not follow the proper methodology of talking about the Qur`aan and if you did not follow a proper methodology of talking about the Qur`aan, then you have committed a sin already.
Just by talking about the Qur`aan, without proper knowledge, by giving interpretation of the Qur`aan, without proper knowledge, without proper background, without being qualified to do so, then you have already committed a sin. And since you are commiting a sin, it is very unlikely in most cases that Allaah (swt) will bless you through that sin to give you the right interpretation of the Qur`aan. When you say that Allaah (swt) means this or Allaah (swt) means that, in a specific verse, you are actually speaking or saying something on behalf of Allaah (swt), you are actually speaking about Allaah (swt), and if you are speaking without knowledge ('ilm), this is one of the greatest sins that you could commit.
In fact, Ibn ul Qayyim said that it is the greatest sin. Ibn ul Qayyim said that speaking about Allaah swt without `ilm is the greatest sin that you could commit. He bases it on this verse:
"Qul innamaa Harrama Rabbi-l-fawaaHisha maa DHahara minhaa wa maa baTan, wal-ithma wal-baghya bi ghayri-l-Haqq, wa an tushrikoo bi-Llaahi maa lam yunazzil bihi sulTaanaa, wa an taqoolo 'ala-l-Laahi maa laa ta'lamoon." Translation: "Say: The things that my Lord has indeed forbidden are al-Fawaahishah (great evil sins, every kind of unlawful sexual intercourse, etc.), whether committed openly or secretly, sins (of all kinds), unrighteous oppession, joining partners (in worship) with Allaah for which He has given no authority and saying things about Allaah of which you have no knowledge."
In discussing this verse, he says, first of all there are some sins which are haraam li-dhaatihi, forbidden due to their own evil nature, and (others which are) haraam li ghairihi, which are forbidden because they lead to some evil or have some evil in them. And he said with respect to this verse, all of these four, they are haraam in dhaatihi, they are haraam in their own essence, because of the evil in them. Continuing his discussion, he said that Allaah (swt) first mentions al-fawaahishah, and he says this is the least of the sins that He mentions, after that He mentions the sins of transpasses against the truth; this is a greater sin that the first one that Allaah mentioned.
And then He mentioned making shirk [which is even greater than the other two], and finally He mentioned saying things about Allaah (swt) of which you have no knowledge. He is saying that Allaah (swt) is going from from the lesser to the greater [in the above verse]. And the reason, he says, is that this last sin of saying about Allaah (swt) without 'ilm, which is actually what you do when you make tafseer (explanation) without the proper background, without the proper methodology, he says it involves and it includes many things even more than what commiting shirk involves. He says it involves and it includes:
In other words, when you are speaking without 'ilm, in the religion, in things which are related to the religion, then in fact you are changing the religion of Allaah (swt). And in fact, if you continue what he wrote - this is right from 'Madaarij us Saalikeen', 1:372-3 - you find that in fact speaking without `ilm is actually the real source of all kufr and shirk.
He said, for example, the polytheists claim what they are worshipping instead of Allaah (swt) was something to take them closer to Allaah (swt), so the cause of their shirk was saying something about Allaah (swt) without `ilm, something they did not know about Allaah (swt).
Similarly today, the greatest kufr that we have nowadays, among Muslims, but especially among non-Muslims, is secularism and the basis for that is saying that Allaah (swt) doesn't really care about what we do in worldly affairs, or hasn't really given us guidance for worldly affairs, or the Deen that He sent is not meant for daily affairs; all of this is speaking about Allaah without knowledge.
So in fact, it is one of the greatest sins, and Ibn ul Qayyim even included that it is in fact the greatest sin. And he also mentioned that every bid'ah, every innovation, also is based on some statement that has no support from the Qur`aan and Sunnah, in other words every bid`ah also is based on some statement which is actually made without `ilm.
To think about this point even further, about just going to the Qur`aan, and saying, I am a believer - I am pious, I can go to the Qur`aan, and read the Qur`aan, and get its own meaning, if there was any people in the history of mankind who could have said that - maybe we could accept this from them; would be the Companions of the Prophet (saws), for many reasons:
So if anyone could actually make that claim that he has such a pure heart and such a close relationship to Allaah (swt) or such a good understanding of Islaam, that he can go to the Qur`aan and interpret the Qur`aan simply by what his heart tells him or what they used to call ra`ee (personal opinion) - after the Soofees it became 'What the heart tells you,' but originally it was called ra`ee or personal opinion, it would be the Sahaaba, but if we go to the Sahaaba we see that what they understood and what they learned from the Prophet (saw) in fact is the complete opposite. What they learned is that it is absolutely forbidden to speak about the Qur`aan without proper knowledge.
And they made such statements. For example, Abu Bakr (ra) one time said, "What earth would give me place to live and what sky would shade me if I should speak about the Qur`aan with my opinion or by something I do not know."
And 'Umar ibn al Khattaab, he also said, "Beware of using your opinion in religious matters."
And Ibn 'Abbaas, the one who the Prophet (saws) made du'aa for him to understand the Qur`aan, to get the understanding of the Deen, and to be given by Allaah (swt) the understanding of the Qur'aan, he also said, "All that there is to follow and obey is the Book of Allaah and the Sunnah of His Messenger. Whoever makes any statement after these two according to his opinion, then I do not know if you'll find among his good deeds or among his sins."
This is the style of Ibn 'Abbaas, that he made in many statements. Meaning that even if what you did was something good, looks like something good, you will find it among your sins. And at-Tirmidhee, in his Sunan, he said it has been related from some of the people of knowledge, the Sahaaba of the Prophet (saw) and others, that they that they were very strict when it came to speaking about the Qur`aan without 'ilm.
: Slightly adapted from http://www.islaam.com (Transcribed from J. Zarabozo's Usool at-Tafseer tape 1/12)