6 But, returning to the deplorable laws regarding religious confessions and Congregations, We learned with great sorrow that therein, at the beginning, it is openly declared that the State has no official religion, thus reaffirming that separation of State from Church which was, alas, decreed in the new Spanish Constitution. We shall not delay here to repeat that it is a serious error to affirm that this separation is licit and good in itself, especially in a nation almost totally Catholic. Separation, well considered, is only the baneful consequence - as We often have declared, especially in the Encyclical Quas Primas - of laicism, or rather the apostasy of society that today feigns to alienate itself from God and therefore from the Church.
Source: Dilectissima Nobis (Vatican.va)