Tafsir of At-Taghabun 64:12

(And obey Allah and obey the Messenger): The command is repeated for emphasis and to signal the difference between the two forms of obedience in terms of their modality, and to clarify the subject of turning away in His saying, Exalted is He: (But if you turn away)—that is, from obeying the Messenger.

His saying, Exalted is He: (Then there is not upon Our Messenger except the clear notification) is a justification for the omitted consequence that has been replaced by this [statement]. It implies: Then there is no blame upon him, for his duty is nothing but clear notification, and he has fulfilled that to the utmost degree.

The mention of "the Messenger" attributed to the pronoun of majesty (the "Nâ" in "Rasûlinâ")—instead of using a pronoun [such as "Our Messenger" instead of "him"]—is to honor him, peace and blessings be upon him, and to indicate the pivot upon which the ruling turns: that his function, may Allah exalt him and grant him peace, is purely notification. It also serves to further condemn the act of turning away from him. The restriction (hasr) in the statement is relative.