This commandment is held by all Christians as a defining ethical principle and, together with the love of God, as the summation of the whole moral teaching of scripture. Shared with Judaism, from whose scripture it is taken, it is given by Jesus a universal reach that shapes Christian ideals of charity, forgiveness, and care for the vulnerable. Its pairing of neighbour-love with self-love, and its extension to the enemy, mark it as central to how Christianity understands the demand of God upon human conduct.
The tension between loving one's neighbour, and even one's enemy, and the use of force has produced two enduring and opposed Christian traditions. Just war theory, developed by Augustine and refined by Aquinas, holds that love of neighbour can require the restrained use of force to protect the innocent from graver harm. Christian pacifism, represented by the historic peace churches (Mennonites, Quakers, Church of the Brethren) and argued forcefully by Leo Tolstoy in The Kingdom of God Is Within You (1894), holds that Jesus's extension of neighbour-love to the enemy rules out killing even in a just cause, since the command admits no exception for whom one is permitted to harm. Both traditions claim the same text and the same command as their foundation, which is itself evidence of how much interpretive weight the single verse is asked to carry.