Sulh-e-Kul is a Persian phrase that means ‘Peace with all’. I think it is the best interpretation of Islam given by the Sufis, which truly expresses its spirit.
Human life in Islam is held in such high esteem that if even a single human being is killed, that is considered equivalent to the assassination of the whole of mankind. And the protection of a single human life is equivalent to the protection of the whole of mankind. (5:27-32)