ق ل بthe heart, turning

القلب · al-qalb · the heart

• Met in: V1 p3 ¶2: «كتاب شرح عجائب القلب», "the Book of Explaining the Wonders of the Heart"; and ¶6: «وتطهير القلب منه», "and to cleanse the heart from it".
• Dictionary form: قَلْب (corpus lemma, 132 times in the Quran). Plural قُلُوب, on the pattern فُعُول, as in قُلُوبِهِمْ (2:7).
• Pattern: فَعْل (faʿl). The same root gives the verb قَلَبَ, "he turned it over", and تَقَلُّب, "turning about" (corpus lemma, 5 times).
• Meaning here: The heart: not the organ, but the inner self that knows, loves and turns toward Allah or away from Him. The Ihya gives it a whole book (the first of the Quarter of Things that Destroy).

Ibn Faris, Maqāyīs al-Lugha, root قلب, vol 5, p 17

القاف واللام والباء أصلان صحيحان: أحدهما يدل على خالص شيء وشريفه، والآخر على رد شيء من جهة إلى جهة

Two sound origins: one indicates the pure and noblest part of a thing, the other turning a thing from one direction to another. (Both fit the heart: the best part of a person, and the part that turns.)

Urdu bridge

قلب is Urdu too, in the same sense, though everyday Urdu says دل. قلبی (of the heart) and انقلاب (a turning over, a revolution) come from the same root. (to be confirmed)

Quran

168 words from this root (Quranic Arabic Corpus). Most common: قَلْب (heart) ×132, ٱنقَلَبَ (turned back) ×17.

إِلَّا مَنْ أَتَى ٱللَّهَ بِقَلْبٍ سَلِيمٍ

But only one who comes to Allah with a sound heart."

Surah Ash-Shu'araa (26), ayah 89 · Saheeh International

Why this ayah: What counts on the Day of Judgement is the state of the heart, which is what the Ihya is about.

In the Ihya

القلب: 1,626 times in the Ihya, one of its most frequent words.