His Excellency Allamah Khorasani in page 28 of the book “Return to Islam” has interpreted the heart in the sense of the very intellect. The question is that what is the difference between the Quranic words «فؤاد, قلب and لب»? Why the heart has been interpreted as intellect?
«فؤاد, قلب and لب» in the book of God, all three mean intellect; since the intellect means the power of comprehension, and in nobody’s nature has been placed two powers of comprehension; as God has said: ﴿مَا جَعَلَ اللَّهُ لِرَجُلٍ مِنْ قَلْبَيْنِ فِي جَوْفِهِ ۚ﴾ and it is obvious that the plurality of title does not necessitate the plurality of meaning. Yes, it is possible «فؤاد, قلب and لب» be the names for the levels of intellect regarding the amount of its soundness; in the way that «فؤاد» would be its minimum, «قلب» its intermediate, and «لبّ» its maximum; since God has ascribed the «فؤاد» to all mankind consist of those who are good and bad and has said: ﴿وَهُوَ الَّذِي أَنْشَأَ لَكُمُ السَّمْعَ وَالْأَبْصَارَ وَالْأَفْئِدَةَ ۚ قَلِيلًا مَا تَشْكُرُونَ﴾; “It is He who made for you hearing, eyesight, and hearts. Little do you thank” and has said: ﴿وَلِتَصْغَى إِلَيْهِ أَفْئِدَةُ الَّذِينَ لَا يُؤْمِنُونَ بِالْآخِرَةِ﴾; “so that toward it may incline the hearts of those who do not believe in the Hereafter” and He has ascribed «قلب» to all mankind consist of those who are good and bad, but has negated its application from those who are bad and has said: ﴿لَهُمْ قُلُوبٌ لَا يَفْقَهُونَ بِهَا﴾; “they have hearts with which they do not understand” and has said: ﴿أَفَلَمْ يَسِيرُوا فِي الْأَرْضِ فَتَكُونَ لَهُمْ قُلُوبٌ يَعْقِلُونَ بِهَا﴾; “Did they not walk around the earth so that there be hearts for them with which they reason?” and has said: ﴿أَفَلَا يَتَدَبَّرُونَ الْقُرْآنَ أَمْ عَلَى قُلُوبٍ أَقْفَالُهَا﴾; “Do they not contemplate the Qurʾān, or are there their locks on the hearts?!” and He has not ascribed «لبّ» to all mankind, but has only considered it for those who are good and has said: ﴿الَّذِينَ يَسْتَمِعُونَ الْقَوْلَ فَيَتَّبِعُونَ أَحْسَنَهُ ۚ أُولَئِكَ الَّذِينَ هَدَاهُمُ اللَّهُ ۖ وَأُولَئِكَ هُمْ أُولُو الْأَلْبَابِ﴾; “Those who hear every word and follow the best of it; they are the very people God has guided them and they are the very people who are the intellectuals”! With this description, «فؤاد» is the intellect which all mankind possess it and benefit from it, and «قلب» is the intellect which all mankind possess it, but do not benefit from it, and «لبّ» is the intellect which all mankind do not possess it, but only the followers of truth possess it and that is named in book of God as “sound heart”; as He has said: ﴿إِلَّا مَنْ أَتَى اللَّهَ بِقَلْبٍ سَلِيمٍ﴾; “except for him who comes to Allah with a sound heart”.
Regarding your answer about the names of intellect in the Quran, I have a question that I would be grateful if, as always, explain it with your clear and well-founded explanation: what is the meaning of «فؤاد» or the intellect that all mankind possess and use? If all mankind possess this intellect, then what is the reason behind misguidance of many of them? Furthermore, what is the «قلب» or the intellect that everybody has, but only those who are good benefit from it? If those who are bad do not use this intellect, then how do they possess it?!
The meaning of intellect that all mankind possess and benefit from it, is the intellect with which they are being discriminated from the insane and contrive their livelihood, because they all, regardless of their goodness or badness, possess and benefit from such an intellect and if it had not been like this, the system of the world would have been disrupted and the chaos would have encompassed the earth, and the meaning of intellect that all mankind possess but only those who are good benefit from it, is the power and skill of truth cognition that everyone possess, but only good people actualize it, and this is the basis of mankind’s duty and the fairness of good people’s reward and the punishment of others, and the meaning of intellect that only good people possess, is the intellect which has been liberated from the impediments of truth cognition, and has practically reached its cognition, and from here it is understood that «فؤاد، قلب and لب» are three names for an intellect that have been applied to it in three validities and from three respects.