Happy Easter!

[Mystic]

Region/time context - generalization of the people with those beliefs, that the proof had become manifest to them - among them is the argument posed in the verse. They knew very well that God is Independent by which all things depend on (As-Samad) and hence cannot be begotten nor beget himself and understood the various arguments for Tawheed as well as Mohammad's Prophethood.  Since the trinity had dependency on part of the holy spirit and Jesus, it's saying, what would happen if God were to destroy them and all that is in the universe. The truth is God would still exist, and hence, whatever is dependent cannot be said to be the Independent Creator. This verse is emphasizing on one of the reasoning they were aware of but were ignoring.

There was repeated arguments reminding of Tawheed, and the truth was clarified to them, and they knew very well the truth.  They were not only irrational for denying Mohammad, but the Quran showed, they weren't even accepting the clearest reminders in Quran which was towards Tawheed.

However as I said,  the Quran shows polytheists and people of the book only become distinct and divided from believers when the clear proof comes to them.  The clear proof was at that time a Messenger who recites them the signs.