Source: Tafseer Ibn Katheer
Allah then refutes the Christians’ and Jews’ false claims and lies,
(And the Jews and the Christians say, “We are the children of Allah and His loved ones.”) They claim: “We are the followers of Allah’s Prophets, who are His children, whom He takes care of. He also loves us.” The People of the Book claim in their Book that Allah said to His servant Isra’il, “You are my firstborn.” But they explained this statement in an improper manner and altered its meaning. Some of the People of the Book who later became Muslims refuted this false statement saying, “This statement only indicates honor and respect, as is common in their speech at that time.” The Christians claim that `Isa said to them, “I will go back to my father and your father,” meaning, my Lord and your Lord. It is a fact that the Christians did not claim that they too are Allah’s sons as they claimed about `Isa. Rather this statement by `Isa only meant to indicate a closeness with Allah. This is why when they said that they are Allah’s children and loved ones, Allah refuted their claim,
(Say, “Why then does He punish you for your sins”) meaning, if you were truly as you claim, Allah’s children and loved ones, then why did He prepare the Fire because of your disbelief, lies and false claims
(Nay, you are but human beings, of those He has created,) Allah states: you are just like the rest of the children of Adam, and Allah is the Lord of all His creation,
(He forgives whom He wills and punishes whom He wills.) Allah does what He wills, there is none who can escape His judgement, and He is swift in reckoning.
(And to Allah belongs the dominion of the heavens and the earth and all that is between them;) Therefore, everything is Allah’s property and under His power and control,
(and to Him is the return.) In the end, the return will be to Allah and He will judge between His servants as He will, and He is the Most Just Who is never wrong in His judgment.