Matter of hearts!

[In] al-Hakeem al-Tirmidhi’s example, the sadr is where one’s Islam rests, a general term. The qalb is the place where certainty and faith (al-eemaan) rests, and it is like the eye, which is a term applied to all of its component parts that see. The fuaad is the place of witnessing and seeing, like the pupil to the eye, and finally, the lubb is the innermost place where tawheed rests, the light in the vision of the eye. The Ulul-albaab, those people of true hearts, peel away the skin of a metaphorical existence, and subsist in the core (lubb) of the true existence, which is only through the belief in the Oneness of Allah Ta’ala.

Read "Difference Between the “Heart” (Qalb), “Kindling Heart” (fuaad), and the “Pure Intellect” (lubb)" @ SeekersGuidance