Peace Hamzah.
I know you are asking brother Joseph,but I hope you do not mind me giving my understanding.
Of course you can disregard,if you wish.
The clue is in the theme of the surah( Alzukhruf/Ornaments), this theme is "Serve/worship GOD Alone,no idols!
GOD is saying He knows they are saying "Jesus is the son of GOD". So 43:81 is say to them ( Muhammed) that if that was true,then I would still be taking "this son "as an idol like you are instead of correcting you. i.e I would not be preaching this Qoran/the truth that "GOD is unique", serve/worship GOD Alone, He has not begotten a son...etc Be He glorified!
In other words my message /deen would be the same as yours?
Of course that is my understanding.
GOD bless you.
Peace.