Short answer
With respect and honest disagreement. The Quran calls Christians People of the Book, says they are the nearest in affection to the believers, and praises the humble and devout among them. It also rejects the Trinity and the divinity of Jesus, and invites Christians to worship the one God. Muslims are told to be just and kind to them.
Christians are Ahl al-Kitab in the Hanafi school. Their properly slaughtered meat is lawful, a Muslim man may marry a chaste Christian woman, though Hanafi muftis discourage it today, and kindness, gifts, trade and friendly relations are permitted. Taking them as protectors in matters of religion over the believers is not allowed.
The four schools agree on this.
Explanation
The Quran speaks of Christians warmly in several places. It says the nearest in affection to the believers are those who say we are Christians, because among them are priests and monks who are not arrogant. It describes some who weep when they hear the Quran because they recognise the truth in it. And it says plainly that the People of the Scripture are not all the same: some stand in prayer at night and hasten to good deeds.
History shows the same warmth. When the early Muslims were persecuted in Makkah, the Prophet ﷺ sent them to Abyssinia under a just Christian king, the Najashi, who protected them. When the Najashi died, the Prophet ﷺ told the Companions to pray for their brother. Waraqa ibn Nawfal, a Christian scholar and Khadijah's cousin, was among the first to confirm the Prophet's ﷺ calling.
The disagreement is real and Muslims do not hide it. The Quran rejects the Trinity, the belief that Jesus is God or the Son of God, and the crucifixion. But it asks Muslims to discuss these things only in the best way, and to call Christians to a word that is fair between us: to worship none but Allah.
In daily life, Muslims love Jesus and Mary, can be good friends, neighbours and colleagues with Christians, eat with them and do business with them. The Prophet ﷺ said a Christian who believes in his own prophet and then in Muhammad ﷺ receives a double reward. See what Islam and Christianity have in common and friendship with non-Muslims.
The evidence
Quran, Surah Al-Maaida 5:82
۞ لَتَجِدَنَّ أَشَدَّ ٱلنَّاسِ عَدَٰوَةًۭ لِّلَّذِينَ ءَامَنُوا۟ ٱلْيَهُودَ وَٱلَّذِينَ أَشْرَكُوا۟ ۖ وَلَتَجِدَنَّ أَقْرَبَهُم مَّوَدَّةًۭ لِّلَّذِينَ ءَامَنُوا۟ ٱلَّذِينَ قَالُوٓا۟ إِنَّا نَصَٰرَىٰ ۚ ذَٰلِكَ بِأَنَّ مِنْهُمْ قِسِّيسِينَ وَرُهْبَانًۭا وَأَنَّهُمْ لَا يَسْتَكْبِرُونَ ﴿٨٢﴾
You will surely find the most intense of the people in animosity toward the believers [to be] the Jews and those who associate others with Allah; and you will find the nearest of them in affection to the believers those who say, "We are Christians." That is because among them are priests and monks and because they are not arrogant.
The Quran describes Christians as the closest in affection to Muslims.
Quran, Surah Aal-i-Imraan 3:113
۞ لَيْسُوا۟ سَوَآءًۭ ۗ مِّنْ أَهْلِ ٱلْكِتَٰبِ أُمَّةٌۭ قَآئِمَةٌۭ يَتْلُونَ ءَايَٰتِ ٱللَّهِ ءَانَآءَ ٱلَّيْلِ وَهُمْ يَسْجُدُونَ ﴿١١٣﴾
They are not [all] the same; among the People of the Scripture is a community standing [in obedience], reciting the verses of Allah during periods of the night and prostrating [in prayer].
The Quran praises the devout among the People of the Book.
Quran, Surah Al-Ankaboot 29:46
۞ وَلَا تُجَٰدِلُوٓا۟ أَهْلَ ٱلْكِتَٰبِ إِلَّا بِٱلَّتِى هِىَ أَحْسَنُ إِلَّا ٱلَّذِينَ ظَلَمُوا۟ مِنْهُمْ ۖ وَقُولُوٓا۟ ءَامَنَّا بِٱلَّذِىٓ أُنزِلَ إِلَيْنَا وَأُنزِلَ إِلَيْكُمْ وَإِلَٰهُنَا وَإِلَٰهُكُمْ وَٰحِدٌۭ وَنَحْنُ لَهُۥ مُسْلِمُونَ ﴿٤٦﴾
And do not argue with the People of the Scripture except in a way that is best, except for those who commit injustice among them, and say, "We believe in that which has been revealed to us and revealed to you. And our God and your God is one; and we are Muslims [in submission] to Him."
Disagreement must be expressed with courtesy.
Sahih al-Bukhari 97
Sahih... رجل من أهل الكتاب آمن بنبيه وآمن بمحمد ...
"A man of the People of the Book who believed in his prophet and then believed in Muhammad will have a double reward."
Islam honours the faith a Christian already had.
Sahih al-Bukhari 1327
Sahih... النجاشي صاحب الحبشة يوم الذي مات فيه فقال استغفروا لأخيكم ...
"Ask forgiveness for your brother."
The Prophet ﷺ said this on the death of the Najashi, the king who had protected the early Muslims.
Where the ruling is recorded
- al-Hidaya, Kitab al-Nikah, the chapter on women one may not marry. Marriage to a chaste woman of the People of the Book is valid.
- al-Hidaya, Kitab al-Dhaba'ih. The slaughter of a Jew or Christian is lawful when its conditions are met.
Checked by our team. For a more accurate answer to your own situation, consult a scholar. Quran translation by Sahih International. Hadith Arabic from the standard editions of the six books and the Muwatta, with gradings as recorded there; the English is our own rendering. Spotted a mistake? Tell us.