3 Full of solicitude for this union, we point out the dangers which threaten it arising from certain controversies concerning public law; a subject which, amongst you, engenders a strong difference of feeling. These controversies have for their object the necessity or opportuneness of conforming to the prescriptions of Catholic doctrine the existing forms of government, based on what is commonly called modern law. Most assuredly we, more than any one, ought heartily to desire that human society should be governed in a Christian manner, and that the divine influence of Christ should penetrate and completely impregnate all orders of the State. From the commencement of our Pontificate we manifested, without delay, that such was our settled opinion; and that by public documents, and especially by the Encyclical Letters we published against the errors of Socialism, and, quite recently, upon the Civil Power. Nevertheless, all Catholics, if they wish to exert themselves profitably for the common good, should have before their eyes and faithfully imitate the prudent conduct which the Church herself adopts in matters of this nature: she maintains and defends in all their integrity the sacred doctrines and principles of right with inviolable firmness, and applies herself with all her power to regulating the institutions and the customs of public order, as well as the acts of private life, upon these same principles. Nevertheless, she observes in this the just measure of time and place; and, as commonly happens in human affairs, she is often constrained to tolerate at times evils that it would be almost impossible to prevent, without exposing herself to calamities and troubles still more disastrous.
Source: Licet Multa (Vatican.va)