Rorate Caeli has a post on Pius XII's last encyclical. The text of the encyclical.

4. If we weigh carefully the causes of today's crises and those that are ahead, we shall soon find that human plans, human resources, and human endeavors are futile and will fail when Almighty God - He who enlightens, commands, and forbids; He who is the source and guarantor of justice, the fountainhead of truth, the basis of all laws - is esteemed but little, denied His proper place, or even completely disregarded. If a house is not built on a solid and sure foundation, it tumbles down; if a mind is not enlightened by the divine light, it strays more or less from the whole truth; if citizens, peoples, and nations are not animated by brotherly love, strife is born, waxes strong, and reaches full growth.

5. It is Christianity, above all others, which teaches the full truth, real justice, and that divine charity which drives away hatred, ill will, and enmity. Christianity has been given charge of these virtues by the Divine Redeemer, who is the way, the truth, and the life,[2] and she must do all in her power to put them to use. Anyone, therefore, who knowingly ignores Christianity - the Catholic Church - or tries to hinder, demean, or undo her, either weakens thereby the very bases of society, or tries to replace them with props not strong enough to support the edifice of human worth, freedom, and well-being.

6. There must, then, be a return to Christian principles if we are to establish a society that is strong, just, and equitable. It is a harmful and reckless policy to do battle with Christianity, for God guarantees, and history testifies, that she shall exist forever. Everyone should realize that a nation cannot be well organized or well ordered with religion.

7. As a matter of fact, religion contributes more to good, just, and orderly life than it could if it had been conceived for no other purpose than to supply and augment the necessities of mortal existence. For religion bids men live in charity, justice, and obedience to law; it condemns and outlaws vice; it incites citizens to the pursuit of virtue and thereby rules and moderates their public and private conduct. Religion teaches mankind that a better distribution of wealth should be had, not by violence or revolution, but by reasonable regulations, so that the proletarian classes which do not yet enjoy life's necessities or advantages may be raised to a more fitting status without social strife.