And if Allah willed, He could have made them [of] one religion, (42:8)

Almuntakhab Fi Tafsir Alquran Alkarim

Had Allah willed, He would have made them one conjoint body united in feeling and in thought, but He extends His mercy to whom He will, whereas the wrongful of actions have no tutelary friend or guardian nor can any one afford them help

Tafseer Tafheem-ul-Quran by Syed Abu-al-A'la Maududi

(42:8) If Allah had so willed, He could have made them all a single community. But He admits whomsoever He pleases into His Mercy. As to those given to wrong-doing, they shall have none as protector or helper. *11

And if Allah willed, He could have made them [of] one religion, meaning

*11) This theme has three objects in this context:
First, it is meant to instruct and console the Holy Prophet, as if to say: "Do not grieve so much at the ignorance and deviation of the disbelievers of Makkah and their stubbornness and obduracy. It is Allah's will that man should be granted the freedom of choice and action: then whoever desires to have guidance should be given guidance, and whoever wants to remain. astray should be allowed to go astray. Had this not been Allah's will, there was no need whatever of sending the Prophets and the Book; for this only a creative hint of Allah Almighty's was enough: all human beings would have become as obedient as the rivers, mountains, trees, stones, and alI other creatures. " (In this connection, please also see AI-An'am: 35-36, 107).
Secondly, its addressees arc all those people who were involved in the confusion, and even now are, that if Allah really had wanted to show guidance to human beings and He did not like the differences of creed and practice that were prevalent among the people, and wanted to have the people adopt the way of the Faith and Islam, there was no need of the Revelation and the Book and the Prophethood. He could have easily achieved this object by creating everyone a believer and Muslim by birth. Another result of this confusion was also this reasoning: "When Allah has not done so, the different ways that we are following, are approved by Him, and whatever we are doing, is according to His wilt. Therefore, nobody has any right to object to it. " (To remove this misunderstanding also this theme has been mentioned at several places in the Qur'an. Please see Al-An'am: 112, 137, 148-149; Yunus : 99; Hud: 118-119; An-Nahl: 9, 35 and the relevant E.N.'s).
Thirdly, its object is to make the believers realize the truth about the difficulties that one generally faces in the way of preaching religion and reforming the people. Those people who do not understand the reality of the God, given freedom of choice and will and of the resulting differences of temperament and methods, sometimes become despondent at the slow progress of the reformatory work and wish that some supernatural things should appear from Allah, which should change the hearts of the people, and are sometimes inclined to adopt unsound methods of bringing about reformation, owing to excessive enthusiasm. (For this object also this theme has occurred at some places in the Qur'an, for which see Ar-Ra'd: 31, An-Nahl: 91-93).
To highlight these objects a very important theme has been expressed in these brief sentences. Allah's real vicegerency in the world and His Paradise in the Hereafter is not an ordinary blessing, which may be distributed over creatures of the rank of the earth and stones and donkeys and horses as a common blessing. This is indeed a special blessing and a blessing of a very high order for which even the angels were not considered fit. That in why Allah created man as a creature endowed with power and authority and placed vast means of His earth under his control and blessed him with these special powers so that he may pass through the test, success in which alone can entitle a servant to His blessings. This blessing, is Allah's own; no one has a monopoly over it, nor can anyone claim to have it on the basis of a personal right, nor has anyone the power to take it by force. He who presents service before Allah, who takes Him as his Guardian and comes under His protection, alone can have it. Then Allah blesses him with help, guidance and grace to pass this test, so that he may enter His Mercy. As for the unjust Tnan who turns away from Allah Himself and instead takes others as his patrons, Allah-Has no need that he should become his guardian by force. And the others whom He takes as his guardians do not possess any knowledge and power and authority that they may enable him to achieve success by dint of their guardianship of him.
 

And if Allah willed, He could have made them [of] one religion, meaning in Urdu

اگر اللہ چاہتا تو اِن سب کو ایک ہی امت بنا دیتا، مگر وہ جسے چاہتا ہے اپنی رحمت میں داخل کرتا ہے، اور ظالموں کا نہ کوئی ولی ہے نہ مدد گار