Tafsir of Al-Baqarah 2:147

(The Truth is from your Lord): This is a resumption of speech intended to refute those who conceal [the truth] and to confirm the matter of the Messenger of Allah, may Allah the Exalted bless him and grant him peace; hence, it is disconnected [from the previous sentence].

(The Truth): It is either a subject (mubtada’) whose predicate (khabar) is the prepositional phrase [that follows]. The alif-lam (definite article) is either for specific reference (‘ahd), pointing to what the Prophet, may Allah the Exalted bless him and grant him peace, brought—and it is mentioned with a noun rather than a pronoun to emphasize its authenticity and to establish it firmly—or it is for the generic (jins), which serves to restrict the genus of "Truth" to what has been established by Allah. That is, [it means] that "the Truth" is that which you are upon, and nothing else—unlike that which the People of the Scripture are upon.

Alternatively, it is the predicate of an omitted subject, meaning: "It is the Truth" or "This is the Truth." And (from your Lord) is a second predicate, or a confirming state (hal), in which case the alif-lam is for the generic, as in [the verse] "This is the Book." Its meaning is that what they conceal is the Truth, not what they claim and allege. In this case, there is no meaning for specific reference (‘ahd), as that would lead to redundancy and would require forced interpretation.

Imam Ali, may Allah the Exalted honor his countenance, read (The Truth) in the accusative case (nasb), as the object of [an implied verb] "they know," or as a substitution (badal), with (from your Lord) being a state (hal) derived from it. Through this, there is a distinction from the first [reading], even if the wording is identical. It is also permitted that the accusative case is due to an implied verb, such as "adhere to." Mentioning the attribute of Lordship along with the possessive [pronoun] contains a manifest display of kindness towards him, may Allah the Exalted bless him and grant him peace.

(So do not be among the doubters): That is, [do not be] among those who doubt or hesitate regarding their concealment of the Truth while knowing it, or regarding the fact that it is (from your Lord). It is not intended as a prohibition for the Messenger, may Allah the Exalted bless him and grant him peace, because a prohibition of something necessitates that it is occurring or expected from the one being forbidden, and that is not expected from the station of the Prophetic presence, may Allah the Exalted bless him and grant him peace; thus, there would be no benefit in forbidding him. Furthermore, what one is obligated to do must be voluntary, and doubt and hesitation are not things that occur by intention and choice.

Rather, the intention is either to verify the matter—that it is of such a nature that no one, whoever they may be, could doubt it—or it is a command to the Ummah to acquire the knowledge that removes what was forbidden. Thus, the prohibition is made a metaphor for that command, and in attributing the doubt of the Ummah to him, may Allah bless him and grant him peace, there is an evident exaggeration. You may also say: "Doubt and its likes, although not within one's power to acquire, are within one's power to remove or prevent from remaining," and perhaps the prohibition of it is in this regard. This is why Allah the Exalted said: (So do not be among the doubters) instead of "do not doubt" (fala tamtar). Whoever thinks that the origin of the difficulty lies in the "being" (kawn)—because it is that which is not within one's power to acquire, and therefore should not be forbidden, unlike doubt and hesitation—has not presented anything substantial.