and let him not associate anyone in the worship of his Lord—that is, he must not perform his deeds for show.

Aḥadan (“anyone”): an indefinite noun occurring in a negative statement, and therefore it encompasses every single being, whoever he may be.

Overall meaning: Allah commands His Prophet ﷺ to tell the people that he is a human being like them in his humanness, possessing nothing of lordship or divinity. His task is simply to convey what Allah reveals to him, and the most important of that revelation is that the One truly worthy of worship is a single Deity—Allah—so it is impermissible to associate anyone with Him in worship. All of mankind must return to Him on the Day of Resurrection, and whoever hopes for deliverance on that Day from Allah’s punishment must prepare for it with deeds that are free from every trace of polytheism and that conform to the law He has laid down.

Connection of the verse to the chapter: the verse commands that one’s deeds be purified from every form of polytheism, of which ostentation is one.

Lessons derived from the verse:
1- The bedrock of the religion is to devote worship exclusively to Allah.
2- Ostentation is a type of polytheism.
3- The polytheism committed by the idolaters is polytheism in worship.
4- It is not permissible to worship anyone alongside Allah—neither idols, nor prophets and the righteous, nor anyone else.