Why are kafir najis. Isn’t it an insult? Isn’t it similar with caste system in India where dalits are untouchable ? What is the philosophy behind it?

The literal meaning of 'kufr' is 'to conceal' or 'to hide'. It also means 'disobedience' or 'thanklessness'. Shia’s grand jurisprudents have said that one who denies the oneness of God or associates anyone with Him is a kafir (disbeliever). There are other meanings and instances for kufr (disbelief) which have been mentioned in the treatises written by Muslim scholars and which we do not mention here for the sake of brevity.

As for the impurity of a kafir, Muslim scholars rely on the Quranic verse which says, “Verily, the pagans are impure…”. Shia jurisprudents are almost unanimous about the impurity and uncleanness of disbelievers.

However, when it comes to the People of the Book (Christians and Jews), they hold diverse views; some say that they are ritually and essentially pure. That is to say, if we know that they do not have any physical contact with impure things and have not used them either, then they are not impure.

In any rate, if it is said that this ruling or injunction is an insult to them, it should be said that, first of all, the reason behind Islam’s injunction about the disbelievers’ impurity could be considered as ‘politically motivated’.

Thus, we can say that the purpose behind this injunction is to prevent Muslims from associating with them so that Muslims may not be influenced by their destructive thoughts.