And indeed, your Lord surely knows what their chests conceal

Meaning: what they hide of secrets, among which is their enmity toward you.

And what they declare

Meaning: and what they manifest of speech and actions, among which is what has been recounted regarding them. Thus, the delay of their punishment is not due to their condition being hidden from Him, Glory be to Him; rather, He will recompense them for that. Actions of the heart—when they are of the nature of love, hatred, belief, disbelief, or a firm resolve toward obedience or disobedience—are things for which one is recompensed.

The verse serves as an indication that they possess ugly deeds other than those which have been recounted regarding them. The presentation of concealment (before declaration) is to manifest the intended meaning that the hidden and the manifest are equal in His knowledge, Majestic and Exalted is He; or because the internal states of the chests are the cause for what appears upon the limbs.

And as an indication of the corruption of their chests, which is the origin of all their actions, the noble structure of the verse preferred this over saying: "And indeed, your Lord knows what they conceal and what they declare."

Ibn Muḥayṣin, Ḥumayd, and Ibn al-Sumayqa‘ recited it as takinna (تَكُنَّ), with a fatḥah on the tā’ and a ḍammah on the kāf, derived from kanna al-shay’, meaning to cover and hide a thing.