In his inaugural encyclical Ubi Arcano Dei Pius XI condemns a phenomenon he calls Social Modernism.
“Many believe in or claim that they believe in and hold fast to Catholic doctrine on such questions as social authority, the right of owning private property, on the relations between capital and labour, on the rights of the labouring man, on the relations between Church and State, religion and country, on the relations between the different social classes, on international relations, on the rights of the Holy See and the prerogatives of the Roman Pontiff and the Episcopate, on the social rights of Jesus Christ, Who is the Creator, Redeemer, and Lord not only of individuals but of nations. In spite of these protestations, they speak, write, and, what is more, act as if it were not necessary any longer to follow, or that they did not remain still in full force, the teachings and solemn pronouncements which may be found in so many documents of the Holy See, and particularly in those written by Leo XIII, Pius X, and Benedict XV. There is a species of moral, legal, and social modernism which We condemn, no less decidedly than We condemn theological modernism.”
As Modernism is (according to St Pius X) ‘the synthesis of all heresies’ it is unsurprising that any given heresy might be styled a form of Modernism. Still it is instructive to consider why particularly the principles of theological Modernism should give rise to the rejection of the Social Kingship of Christ.
Modernism is most easily understood in terms of the definition of faith which the Oath Against Modernism requires its adherents to reject and that which is requires them to accept. The Modernist definition of faith according to the Oath is:
“a blind sentiment of religion welling up from the depths of the subconscious under the impulse of the heart and the motion of a will trained to morality”
The orthodox definition in contrast is:
“ a genuine assent of the intellect to truth received by hearing from an external source. By this assent, because of the authority of the supremely truthful God, we believe to be true that which has been revealed and attested to by a personal God, our creator and lord.”
The reason for this is that Modernism is in essence the naturalisation of the supernatural order. In place of faith preached by the Church to the individual and assented to by his intellect moved by the will under grace we have an innate religious sense that arises from human nature itself and is simply articulated through Catholicism or through some other religious system. The articles and the intellectual content of the faith are instrumental to the expression of this sense and may and will need to be modified to fit with the different needs of successive eras and diverse cultures. As a consequence of this Modernist doctrine one must hold that salvation outside of the Church and without explicit faith in Christ is widespread (rather than impossible).
The reason this takes an axe to the Social Kingship of Christ is that the authority of the Church over all men and all spheres of human activity is founded upon the absolute necessity for salvation of the truths which the Church alone authoritatively teaches and the moral necessity for salvation of the other means given to her to bring men to their supernatural end.
This is made very clear by Pius XI in his splendid encyclical on Christian Education Divini Illius Magistri.
“…in faith and morals, God Himself has made the Church sharer in the divine Magisterium and, by a special privilege, granted her immunity from error; hence she is the mistress of men, supreme and absolutely sure, and she has inherent in herself an inviolable right to freedom in teaching.’ By necessary consequence the Church is independent of any sort of earthly power as well in the origin as in the exercise of her mission as educator, not merely in regard to her proper end and object, but also in regard to the means necessary and suitable to attain that end. Hence with regard to every other kind of human learning and instruction, which is the common patrimony of individuals and society, the Church has an independent right to make use of it, and above all to decide what may help or harm Christian education. And this must be so, because the Church as a perfect society has an independent right to the means conducive to its end, and because every form of instruction, no less than every human action, has a necessary connection with man’s last end, and therefore cannot be withdrawn from the dictates of the divine law, of which the Church is guardian, interpreter and infallible mistress.”
The dea that the truths of the faith are merely instrumental means of expression for a need and a sense innate to all men obviously utterly destroys the basis for the Church’s authority over all aspects of every human life and so the Kingship of Christ.
This is why there is an inseparable link between the denial that explicit faith in Christ is necessary for salvation for all human beings who have attained the age of reason (a consequence of theological modernism) and the rejection of the Church’s teaching on the social and civil orders. This is also why those many ‘Catholic’ theologians and journalists who support the Church’s conservatism but reject “traditional Catholic doctrine on the moral duty of men and societies toward the true religion and toward the one Church of Christ” while purporting to accept her theological doctrines, are more dangerous as allies than many an open liberal enemy.