12 Wherefore, that We may above all things, and in every possible way, maintain the rights and freedom of this holy see, We shall never cease to strive that Our authority may meet with due deference; that obstacles may be removed which hamper the free exercise of Our ministry and that We may be restored to that condition of things in which the design of God's wisdom had long ago placed the Roman Pontiffs. We are moved to demand this restoration, venerable brethren, not by any feeling of ambition or desire of supremacy, but by the nature of Our office and by Our sacred promise confirmed on oath; and further, not only because this sovereignty is essential to protect and preserve the full liberty of the spiritual power, but also because it is an ascertained fact that, when the temporal sovereignty of the apostolic see is in question, the cause of the public good and the well-being of all human society in general are also at stake. Hence, We cannot omit, in the discharge of Our duty, which obliges Us to guard the rights of holy Church, to renew and confirm in every particular by this Our letter those declarations and protests which Pius IX,(5) of sacred memory, Our predecessor, on many and repeated occasions published against the seizing of the civil sovereignty and the infringement of rights belonging to the Catholic Church. At the same time We address ourselves to princes and chief rulers of the nations, and earnestly beseech them in the august name of the Most High God, not to refuse the Church's aid, proffered them in a season of such need, but with united and friendly aims, to join themselves to her as the source of authority and salvation, and to attach themselves to her more and more in the bonds of hearty love and devotedness. God grant that-seeing the truth of Our words and considering within themselves that the teaching of Christ is, as Augustine used to say, "a great blessing to the State, if obeyed,"(6) and that their own peace and safety, as well as that of their people, is bound up with the safety of the Church and the reverence due to her - they may give their whole thought and care to mitigating the evils by which the Church and its visible head are harassed, and so it may at last come to pass that the peoples whom they govern may enter on the way of justice and peace, and rejoice in a happy era of prosperity and glory.
Source: Inscrutabili Dei Consilio (Vatican.va)