Tafsir of An-Nahl 16:82

(But if they turn away): This is a past tense verb employing the method of iltifat (shift) from address to the third person. The speech is directed toward the Messenger of Allah (may Allah exalt him and grant him peace) as a consolation for him (peace and blessings be upon him). It means: if they persist in turning away, shunning, and refusing to accept the clear proofs presented to them, (then upon you is only the clear notification).

(Then it will not harm you): Because your duty is to provide the clarifying or clear notification, and you have fulfilled it to the extent that nothing more can be added. It is a case of placing the cause in the place of the effect. Ibn Atiyyah said: The implied meaning is that if they turn away, you are not capable of creating faith in their hearts; therefore, upon you is only the notification, not the creation of faith.

It has been suggested that (tawallaw) might be a present tense verb with one of its two tas omitted, originating as tatawallaw, in which case there is no shift. However, it has been objected that this does not clearly link the consequence to the condition without forced interpretation, which is why some verifiers have disregarded it. In the expression using the form of taf’il (the stem tawallaw), there is an indication, as has been said, that the primordial nature (fitrah) inherently invites one to turn toward Allah Almighty, and that turning away occurs only through a type of affectation and struggle.