From Pope Pius XII’s encyclical Mystici Corporis Christi (1943):
We have been no less consoled to know that with spontaneous generosity a fund has been created for the erection of a church in Rome to be dedicated to our saintly predecessor and patron, Eugene I. At this temple, to be built by the wish and through the liberality of all the faithful, will be a lasting memorial of this happy event, so We desire to offer this Encyclical Letter in testimony of Our gratitude. It tells of those living stones which rest upon the living cornerstone, which is Christ, and are built together into a holy temple, far surpassing any temple built by hands, into a habitation of God in the Spirit.4
But the chief reason for Our present exposition of this sublime doctrine is Our solicitude for the souls entrusted to Us. Much indeed has been written on this subject; and We know that many today are turning with greater zest to a study which delights and nourishes Christian piety. This, it would seem, is chiefly because a revived interest in the sacred liturgy, the more widely spread custom of frequent Communion, and the more fervent devotion to the Sacred Heart of Jesus practiced today, have brought many souls to a deeper consideration of the unsearchable riches of Christ which are preserved in the Church. Moreover, recent pronouncements on Catholic Action, by drawing closer the bonds of union between Christians and between them and the ecclesiastical hierarchy and especially the Roman Pontiff, have undoubtedly helped not a little to place this truth in its proper light. Nevertheless, while We can derive legitimate joy from these considerations, We must confess that grave errors with regard to this doctrine are being spread among those outside the true Church, and that among the faithful, also, inaccurate or thoroughly false ideas are being disseminated which turn minds aside from the straight path of truth.
4 Cf. Eph., II, 21-22; I Peter, II, 5.
— Mystici Corporis Christi 7-8