This excerpt is taken from Sheikh Muhammad Iqbal Kilani's book "Al-Wala Wal Bara".
لا یمکن ولاء بین الکفار والمسلمین
Muslims and disbelievers are two different groups, in which unity or friendship is not possible.
[قُلۡ یٰۤاَیُّہَا الۡکٰفِرُوۡنَ]،[لَاۤ اَعۡبُدُ مَا تَعۡبُدُوۡنَ]،[وَ لَاۤ اَنۡتُمۡ عٰبِدُوۡنَ مَاۤ اَعۡبُدُ]،[وَ لَاۤ اَنَا عَابِدٌ مَّا عَبَدۡتُّمۡ]،[وَ لَاۤ اَنۡتُمۡ عٰبِدُوۡنَ مَاۤ اَعۡبُدُ]،[لَکُمۡ دِیۡنُکُمۡ وَلِیَ دِیۡنِ]
(O Muhammad!) Say, O disbelievers! I do not worship what you worship, nor do you worship what I worship, nor will I be a worshiper of what you worship, nor will you be worshipers of what I worship. For you is your religion, and for me is my religion.
Reference: (Surah Al-Kafirun: 1 to 6)
❀ [عَنْ جَرِیْرِبْنِ عَبْدِاللّٰہِ رَضی اللّٰه عنہ قَالَ: قَالَ رَسُوْلُ اللّٰہِ صلی اللّٰه علیہ وسلم لاَ تَرَایَا نَارَاہُمَا]
Sayyiduna Jarir bin Abdullah (may Allah be pleased with him) says the Messenger of Allah (peace be upon him) said: The fire of Muslims and disbelievers cannot burn together. This has been narrated by Abu Dawood.
Reference: Sunan Abi Dawood: 2645
The Shariah of Muslims and disbelievers is separate, therefore agreement and unity between them is impossible.
[وَ لَئِنۡ اَتَیۡتَ الَّذِیۡنَ اُوۡتُوا الۡکِتٰبَ بِکُلِّ اٰیَۃٍ مَّا تَبِعُوۡا قِبۡلَتَکَ ۚ وَ مَاۤ اَنۡتَ بِتَابِعٍ قِبۡلَتَہُمۡ ۚ وَ مَا بَعۡضُہُمۡ بِتَابِعٍ قِبۡلَۃَ بَعۡضٍ ؕ]
Bring any sign to those People of the Book; they will not follow your Qiblah, nor is it possible for you to follow their Qiblah. Neither group will be willing to follow the Qiblah of the other.
Reference: (Surah Al-Baqarah:145)
Muslims and disbelievers, even if they are father and son, have separate paths.
[قَالَ اَرَاغِبٌ اَنۡتَ عَنۡ اٰلِہَتِیۡ یٰۤـاِبۡرٰہِیۡمُ ۚ لَئِنۡ لَّمۡ تَنۡتَہِ لَاَرۡجُمَنَّکَ وَ اہۡجُرۡنِیۡ مَلِیًّا]
(In response to the invitation of Prophet Ibrahim) The father said, "O Ibrahim! Have you forsaken my gods? If you do not desist, I will stone you, so be away from me forever."
Reference: (Surah Maryam:46)
There is a distance like east and west between the believers and the disbelievers.
[وَ مَا یَسۡتَوِی الۡاَعۡمٰی وَ الۡبَصِیۡرُ]،[ وَ لَا الظُّلُمٰتُ وَ لَا النُّوۡرُ]،[وَ لَا الظِّلُّ وَ لَا الۡحَرُوۡرُ]،[وَ مَا یَسۡتَوِی الۡاَحۡیَآءُ وَ لَا الۡاَمۡوَاتُ ؕ اِنَّ اللّٰہَ یُسۡمِعُ مَنۡ یَّشَآءُ ۚ وَ مَاۤ اَنۡتَ بِمُسۡمِعٍ مَّنۡ فِی الۡقُبُوۡرِ]
The blind (i.e., disbeliever) and the seeing (i.e., Muslim) are not equal, nor is the one who lives in darkness and the one who lives in light equal, nor is the one who dwells in shade (in the Hereafter) and the one who dwells in heat equal, nor are the living (Muslims) and the dead (disbelievers) the same. Allah makes hear whom He wills, but those in the graves (O Muhammad, peace be upon him!) cannot be made to hear.
Reference: (Surah Fatir:19-22)
Disbelievers consider Muslims misguided, and Muslims consider disbelievers misguided.
[اِنَّ الَّذِیۡنَ اَجۡرَمُوۡا کَانُوۡا مِنَ الَّذِیۡنَ اٰمَنُوۡا یَضۡحَکُوۡنَ]،[ وَ اِذَا مَرُّوۡا بِہِمۡ یَتَغَامَزُوۡنَ]،[وَ اِذَا انۡقَلَبُوۡۤا اِلٰۤی اَہۡلِہِمُ انۡقَلَبُوۡا فَکِہِیۡنَ]،[وَ اِذَا رَاَوۡہُمۡ قَالُوۡۤا اِنَّ ہٰۤؤُلَآءِ لَضَآلُّوۡنَ]
The sinful people used to mock those who believed in this world; when they passed by them, they would wink and point at them; when they turned to their families, they would turn back enjoying themselves; and when they saw the Muslims, they would say, "These are misguided people."
Reference: (Surah Al-Mutaffifin:29-32)
❀ [فَوَیۡلٌ لِّلَّذِیۡنَ کَفَرُوۡا مِنۡ مَّشۡہَدِ یَوۡمٍ عَظِیۡمٍ]،[اَسۡمِعۡ بِہِمۡ وَ اَبۡصِرۡ ۙ یَوۡمَ یَاۡتُوۡنَنَا لٰکِنِ الظّٰلِمُوۡنَ الۡیَوۡمَ فِیۡ ضَلٰلٍ مُّبِیۡنٍ]
Destruction is for those who disbelieved on the Day of Great Gathering, the Day they will come to Us; on that Day they will hear and see well, but today these wrongdoers are in clear error.
Reference: (Surah Maryam:37-38)
The purpose of life for disbelievers and Muslims is different.
[اَلَّذِیۡنَ اٰمَنُوۡا یُقَاتِلُوۡنَ فِیۡ سَبِیۡلِ اللّٰہِ ۚ وَ الَّذِیۡنَ کَفَرُوۡا یُقَاتِلُوۡنَ فِیۡ سَبِیۡلِ الطَّاغُوۡتِ فَقَاتِلُوۡۤا اَوۡلِیَآءَ الشَّیۡطٰنِ ۚ اِنَّ کَیۡدَ الشَّیۡطٰنِ کَانَ ضَعِیۡفًا]
Those who have believed fight in the cause of Allah, and those who disbelieve fight in the cause of Taghut. So fight against the allies of Satan. Indeed, the plot of Satan is weak.
Reference: (Surah An-Nisa:76)
The end of disbelievers and Muslims is also different.
[اَلَّذِیۡنَ کَفَرُوۡا لَہُمۡ عَذَابٌ شَدِیۡدٌ ؕ وَ الَّذِیۡنَ اٰمَنُوۡا وَ عَمِلُوا الصّٰلِحٰتِ لَہُمۡ مَّغۡفِرَۃٌ وَّ اَجۡرٌ کَبِیۡرٌ]
Indeed, those who disbelieve will have a severe punishment, and those who have believed and done righteous deeds will have forgiveness and a great reward.
Reference: (Surah Fatir:7)