Tafsir of At-Tur 52:29

(So remind): Persist in what you are upon regarding reminding [the people] through the verses and the wise remembrance (the Quran) revealed to you, and pay no heed to the falsehoods they invent in their choice [of words].

(For you are not, by the favor of your Lord, a soothsayer): He is the one who tells of the unseen through conjecture. Al-Raghib distinguished the kahin (soothsayer) as one who tells of hidden past events, and the ‘arraf (diviner) as one who tells of future events in the same manner. It is well-known that soothsaying involves seeking assistance from the jinn to report on the unseen. The ba in bi-kahin (a soothsayer) is an augmentative particle for emphasis, meaning: you are not a soothsayer (nor a madman).

There is disagreement regarding the ba in bi-ni’mati (by the favor of). Abu al-Baqa’ said: It is for accompaniment (mulabasa), and the prepositional phrase is in the position of a state (hal), the governing word being kahin or majnun. The meaning is: You are not a soothsayer nor a madman, while accompanied by the favor of your Lord. This is a necessary state because the Prophet (peace and blessings be upon him) was always accompanied by the favor of his Lord, Exalted and Majestic is He.

It has been said: It is for an oath, so "the favor of your Lord" is what is sworn by, and the response to the oath is what is understood from the discourse, which is: "You are not a soothsayer nor a madman." This is like saying: "By Allah, Zayd is not standing," though this view is far-fetched.

The closest view in my estimation is that the ba is for causality (sababiyya), and it relates to the content of the discourse. The meaning is: Soothsaying and madness are negated from you due to the favor of Allah Almighty upon you. This is like saying: "I am not in distress, by the praise of Allah and His enriching me." The intent is to refute the one who says such things and to invalidate their statements regarding him (peace and blessings be upon him). Otherwise, there would be no favor granted to him by the mere negation of what was mentioned, as it is also negated from most people.

It is also said: The favor mentioned consists of the truthfulness of prophecy and the soundness of intellect granted to him, which no one before him was granted. Those who said these things are the disbelievers—may Allah fight them, how are they deluded! Among those who called him a soothsayer was Shaybah ibn Rabi'ah, and among those who called him a madman was 'Uqbah ibn Abi Mu'ayt.