17 What We have said so far demonstrates the supreme importance of religious instruction. We ought, therefore, to do all that lies in our power to maintain the teaching of Christian doctrine with full vigor, and where such is neglected, to restore it; for in the words of Our Predecessor, Benedict XIV, "There is nothing more effective than catechetical instruction to spread the glory of God and to secure the salvation of souls."
Source: Acerbo Nimis (Vatican.va)