Ibn Kathir
Allah directed His Prophet to pre-empt the arguments with the idolators:
قُلْ أَتُحَآجُّونَنَا فِى اللَّهِ
(Say (O Muhammad to the Jews and Christians), "Dispute you with us about Allah) meaning, "Do you dispute with us regarding the Oneness of Allah, obedience and submission to Him and in avoiding His prohibitions,
وَهُوَ رَبُّنَا وَرَبُّكُمْ
(while He is our Lord and your Lord) meaning, He has full control over us and you, and deserves the worship alone without partners.
وَلَنَآ أَعْمَـلُنَا وَلَكُمْ أَعْمَـلُكُمْ
(And we are to be rewarded for our deeds and you for your deeds.) meaning, we disown you and what you worship, just as you disown us. Allah said in another Ayah,
وَإِن كَذَّبُوكَ فَقُل لِّى عَمَلِى وَلَكُمْ عَمَلُكُمْ أَنتُمْ بَرِيئُونَ مِمَّآ أَعْمَلُ وَأَنَاْ بَرِىءٌ مِّمَّا تَعْمَلُونَ
(And if they belie you, say: "For me are my deeds and for you are your deeds! You are innocent of what I do, and I am innocent of what you do!") (10:41), and,
فَإنْ حَآجُّوكَ فَقُلْ أَسْلَمْتُ وَجْهِىَ للَّهِ وَمَنِ اتَّبَعَنِ
(So if they dispute with you (Muhammad ) say: "I have submitted myself to Allah (in Islam), and (so have) those who follow me") (3:20). Allah said about Ibrahim,
وَحَآجَّهُ قَوْمُهُ قَالَ أَتُحَاجُّونِّى فِى اللَّهِ
(His people disputed with him. He said: "Do you dispute with me concerning Allah") (6:80), and,
أَلَمْ تَرَ إِلَى الَّذِى حَآجَّ إِبْرَهِيمَ فِى رِبِّهِ
(Have you not looked at him who disputed with Ibrahim about his Lord (Allah)) (2:258). He said in this honorable Ayah,
وَلَنَآ أَعْمَـلُنَا وَلَكُمْ أَعْمَـلُكُمْ وَنَحْنُ لَهُ مُخْلِصُونَ
(And we are to be rewarded for our deeds and you for your deeds. And we are sincere to Him.) meaning, "We disown you just as you disown us,"
وَنَحْنُ لَهُ مُخْلِصُونَ
(And we are sincere to Him), in worship and submission.
Allah then criticized them in the claim that Ibrahim, the Prophets who came after him and the Asbat were following their religion, whether Judaism or Christianity. Allah said,
قُلْ ءَأَنتُمْ أَعْلَمُ أَمِ اللَّهُ
(Say, "Do you know better or does Allah") meaning, Allah has the best knowledge and He stated that they were neither Jews, nor Christians. Similarly, Allah said in the Ayah,
مَا كَانَ إِبْرَهِيمُ يَهُودِيًّا وَلاَ نَصْرَانِيًّا وَلَكِن كَانَ حَنِيفًا مُّسْلِمًا وَمَا كَانَ مِنَ الْمُشْرِكِينَ
(Ibrahim was neither a Jew nor a Christian, but he was a true Muslim Hanifa (to worship none but Allah alone) and he was not of Al-Mushrikin) (3:67) and the following Ayat. Allah also said,
وَمَنْ أَظْلَمُ مِمَّنْ كَتَمَ شَهَـدَةً عِندَهُ مِنَ اللَّهِ
And who is more unjust than he who conceals the testimony he has from Allah؟ )2:140(. Al-Hasan Al-Basri said, They used to recite the Book of Allah He sent to them that stated that the true religion is Islam and that Muhammad is the Messenger of Allah ﷺ. Their Book also stated that Ibrahim, Ismail, Ishaq, Yaqub and the tribes were neither Jews, nor Christians. They testified to these facts, yet hid them from the people. Allah s statement,
وَمَا اللَّهُ بِغَـفِلٍ عَمَّا تَعْمَلُونَ
(And Allah is not unaware of what you do), is a threat and a warning that His knowledge encompasses every one's deeds, and He shall award each accordingly. Allah then said,
تِلْكَ أُمَّةٌ قَدْ خَلَتْ
(That was a nation who has passed away.) meaning, existed before you,
لَهَا مَا كَسَبَتْ وَلَكُم مَّا كَسَبْتُم
(They shall receive the reward of what they earned, and you of what you earn.) meaning, they bear their deeds while you bear yours,
وَلاَ تُسْـَلُونَ عَمَّا كَانُوا يَعْمَلُونَ
(And you will not be asked of what they used to do) meaning, the fact that you are their relatives will not suffice, unless you imitate their good deeds. Further, do not be deceived by the fact that you are their descendants, unless you imitate them in obeying Allah's orders and following His Messengers who were sent as warners and bearers of good news. Indeed, whoever disbelieves in even one Prophet, will have disbelieved in all the Messengers, especially if one disbelieves in the master and Final Messenger from Allah, the Lord of the worlds, to all mankind and the Jinns. May Allah's peace and blessings be on Muhammad ﷺ and the rest of Allah's Prophets.