Who said it?

Yes, it can be googled. But what's the fun in that?

“The religion of the God who became man has met the religion (for such it is) of man who makes himself God. And what happened? ...The attention of our council has been absorbed by the discovery of human needs (and these needs grow in proportion to the greatness which the son of the earth claims for himself). But we call upon those who term themselves modern humanists, and who have renounced the transcendent value of the highest realities, to give the council credit at least for one quality and to recognize our own new type of humanism: we, too, in fact, we more than any others, honor mankind.

“The Catholic religion is for mankind. In a certain sense it is the life of mankind. It is so by the extremely precise and sublime interpretation that our religion gives of humanity (surely man by himself is a mystery to himself) and gives this interpretation in virtue of its knowledge of God: a knowledge of God is a prerequisite for a knowledge of man as he really is, in all his fullness; for proof of this, let it suffice for now to recall the ardent expression of St. Catherine of Siena, ‘In your nature, Eternal God, I shall know my own.’ The Catholic religion is man’s life because it determines life’s nature and destiny; it gives life its real meaning, it establishes the supreme law of life and infuses it with that mysterious activity which we may say divinizes it.

“We can and must recognize in Christ’s countenance the countenance of our heavenly Father–‘He who sees me,’ Our Lord said, ‘sees also the Father’ (Jn 14:9); our humanism becomes Christianity, and our Christianity becomes centered on God. We may say, to put it differently: a knowledge of man is a prerequisite for a knowledge of God.”