We often hear Shi'ah quoting verses yet without really understanding them. We will see that only our Imam (as) - and Rasululah (saw) - have the knowledge of the Quran and its exegesis - Tafsir - we will present evidence that only them can understand and not our brain.
From Burayd Ibn Mu'awiya who said: "Once I asked Abu Ja'far (as), about the meaning of the following verse: '[...] Say, Allah and those who have the knowledge of the Book are sufficient witness (to my prophecy).' The Imam said, it is a reference to us. Ali is the first among us and the most excellent and the best among us after the Holy Prophet."
6 - علي بن إبراهيم، عن أبيه، ومحمد بن يحيى، عن محمد بن الحسن، عمن ذكره جمعيا عن ابن أبي عمير، عن أبن اذينة، عن بريد بن معاوية قال: قلت لابي جعفر (عليه السلام): " قل كفى بالله شهيدا بيني وبينكم ومن عنده علم الكتاب (6) "؟ قال: إيانا عنى، وعلي أولنا وأفضلنا وخيرنا بعد النبي (صلى الله عليه وآله).
- Usul al-Kafi, Vol.1, Page 229, Hadith Number 6
I heard Aba Abdullah (as) saying: Allah (swt) has made our obedience obligatory in His Book, so do not try to learn from (other) people ignorantly, the secrets of Quran is with us, the booties are ours and the pure part of wealth (Khums) is ours, I do not say to you that we are the people who know the unseen, but we know the Book of Allah (swt) and the Book of Allah (swt) contains everything, Allah (swt) has taught us a knowledge that He hasn't taught anybody else, and a knowledge that His angels and Messengers know, so whatever the angels and His Messengers know we know it.
7 ـ عن بشير الدهان قال. سمعت أبا عبدالله (عليه السلام) يقول: ان الله فرض طاعتنا في كتابه فلا يسمع الناس جهلا، لنا صفو المال ولنا الانفال ولنا كرائم القرآن، ولا أقول لكم إنا أصحاب الغيب، ونعلم كتاب الله وكتاب الله يحتمل كل شئ، ان الله أعلمنا علما لا يعلمه أحد غيره، وعلما قد أعلمه ملئكته ورسله، فما علمته ملئكته ورسله فنحن نعلمه (2).
- Tafsir al-Ayyashi, Vol.1, Page 16, Hadith Number 7
From Abu Basir who said: "About this verse, "In fact, the Quran consists of illustrious verses that exist in the hearts of those who have knowledge [...]" Abu Ja'far (as), said, "O Abu Muhammad, for the sake of Allah, be the judge and tell, of whom is it spoken (so often) between the two front and back covers of the Holy Quran?" I then asked, "Who are they, may Allah keep my soul in service for your cause?" "The Imam said, "Who else can they be other than ourselves ?"
3 - وعنه، عن محمد بن علي، عن عثمان بن عيسى، عن سماعة، عن أبي بصير، قال: قال أبوجعفر (عليه السلام) في هذه الآية: " بل هو آيات بينات في صدور الذين أوتوا العلم ".. ثم قال: أما والله يا أبا محمد ما قال بين دفتي المصحف؟ قلت: من هم؟ جعلت فداك؟ قال: من عسى أن يكونوا غيرنا.
- Usul al-Kafi, Vol.1, Page 214, Page 8
'Allamah al-Majlissi: On the word of Allah, "that exist in the hearts of those who have knowledge" and we are related by his word. Evidence, he used it as evidence (as) on the fact that the Quran can't be understood by other than the Aimah (as) by this verse, because (swt) said "In fact, the Quran consists of illustrious verses that exist in the hearts of those who have knowledge."
قوله تعالى: " في صدور الذين أوتوا العلم " متعلقا بقوله " بينات " فاستدل عليه السلام على أن القرآن لا يفهمه غير الأئمة عليهم السلام بهذه الآية، لأنه تعالى قال: " الآيات بينات في صدور الذين أوتوا العلم "
- Bihar al-Anwar, Vol.23, Page 203
By those proof we can conclude that only Aimah (as) and Rasululah (saw) know the Tafsir of the Quran.
Now let us see if we can actually understand the Quran by ourselves.
I heard Aba 'Abdallah (as) saying, "There is nothing more far from the intellect (3aql) that the Quran."
5 ـ عن عبدالرحمن بن الحجاج قال: سمعت أبا عبدالله (عليه السلام) يقول: ليس ابعد من عقول الرجال من القرآن (1).
- Tafsir al-Ayyashi, Vol.1, Page 17-18, Hadith Number 5
From Abi 'Abdallah (as) who said, "He who judge among two has disbelieved, and who do exegesis (Tafsir) of the Quran by his opinion has disbelieved."
6 ـ عن عمار بن موسى عن أبى عبدالله (عليه السلام) قال: سئل عن الحكومة قال: من حكم برأيه بين اثنين فقد كفر، ومن فسر ـ برأيه ـ آية من كتاب الله فقد كفر (2).
- Tafsir al-Ayyashi, Page 18, Hadith Number 6