What is the ruling on friendship with a Christian, and is it necessary to shun him even though he is a loyal person?

It is not permissible for a Muslim to show allegiance to, love, or befriend a disbeliever, whether they are a Jew, Christian, or anyone else. This is based on the Almighty’s saying: (O you who have believed, do not take My enemies and your enemies as allies, extending to them affection while they have disbelieved in what has come to you of the truth) [Al-Mumtahanah: 1], and His saying: (O you who have believed, do not take the Jews and the Christians as allies. Some of them are allies of one another. And whoever is an ally to them among you – then indeed, he is of them. Indeed, Allah guides not the wrongdoing people) [Al-Ma'idah: 51].

This differs from showing kindness and justice towards peaceful disbelievers, as Allah has permitted kindness and benevolence towards them as long as they have not fought Muslims in religion or expelled them from their homes, based on His saying: (Allah does not forbid you from those who do not fight you because of religion and do not expel you from your homes - from being righteous toward them and acting justly toward them. Indeed, Allah loves those who act justly) [Al-Mumtahanah: 8], provided there is no love in the heart or establishment of friendship.