Tafsir of Al-Anbiya' 21:4

(He said, "My Lord knows the speech in the heaven and the earth"): This is a narration from the Almighty regarding what His Prophet (peace and blessings be upon him) said after the states and sayings of [the disbelievers] were revealed to him, serving as an explanation of the manifestation of their affair and the uncovering of their secrets. The subject of "said" (qāla) is the pronoun referring to him (peace and blessings be upon him), and the sentence following it is its object. This is the recitation of Hamzah, al-Kisa'i, Hafs, al-A'mash, Talhah, Ibn Abi Layla, Ayyub, Khalaf, Ibn Sa'dan, Ibn Jubayr al-Antaki, and Ibn Jarir. The rest of the seven recited it as "Say!" (qul), as a command to His Prophet (peace and blessings be upon him).

"The speech" (al-qawl) is general, encompassing both that which is secret and that which is public. Preferring it over "the secret" is to establish His glory’s knowledge of it through a demonstrative method, while also indicating that His knowledge of both matters is on the same level, with absolutely no difference between them regarding clarity or obscurity, unlike the knowledge of created beings. It is stated in al-Kashf that there is a partial overlap between "secret" and "speech." What is appropriate in this context is to generalize "speech" to include their public utterances, their secrets, and what is even more concealed, as if it were said: "He knows this type and what is higher or lower than it." This contains a hyperbolic expression of the encompassing nature of His knowledge, which is appropriate given the hyperbole they employed in trying to conceal [their talk]. The preference for "secret" over "speech" in other verses is for a subtlety necessitated by those specific contexts; for every station, there is a fitting statement.

The prepositional phrase [in the heaven and the earth] is attached to an implied entity that functions as a state of "the speech," meaning: "existing in the heaven and the earth."

His saying, the Almighty: (And He is the All-Hearing), meaning: of all audible things; (the All-Knowing), meaning: of all knowable things. It is also said: meaning the One who is superlative in knowledge regarding both the audible and the knowable. Included in this, primarily, are their words and their deeds. This is a concluding, parenthetical remark (tadhyil) confirming the content of what preceded it, containing a threat of requital for what they have committed. It is understood from the words of al-Bahr that what preceded it also contains this [threat].