6 To this Crusade We summon all, as to a sacred duty. For Charity is a formal commandment of the evangelical law which Jesus Himself proclaimed as the first and greatest commandment, including and summing up all the others. In days of War and of implacable hatreds, Our immediate predecessor so strongly and so often inculcated Charity that it became the mark of his pontificate. And now We also would put all men in mind of the same most gentle precept: not only because it is the supreme duty, embodying all other precepts of the New Law, but also because it is the highest ideal which can be set before generous souls, desirous of attaining to Christian perfection.
Source: Nova Impendet (Vatican.va)