Saint Jerome is known for his famous assertion that to be ignorant of Scripture is to be ignorant of Christ. This quote, from the Patron of Scripture Studies, is a wonderful reminder to Protestants that the Catholic Church has a long-standing tradition of biblical study and memorization.
Here's the well-known quote in context - from his prologue to the book of Isaiah. Interestingly enough, Saint Jerome calls the prophet Isaiah both an Apostle and Evangelist since he reveals so much about Christ, even before the Savior's birth:
I interpret as I should, following the command of Christ: Search the Scriptures, and Seek and you shall find. Christ will not say to me what he said to the Jews: You erred, not knowing the Scriptures and not knowing the power of God. For if, as Paul says, Christ is the power of God and the wisdom of God, and if the man who does not know Scripture does not know the power and wisdom of God, then ignorance of Scripture is ignorance of Christ.
Therefore, I will imitate the head of a household who brings out of his storehouse things both new and old, and says to his spouse in the Song of Songs: I have kept for you things new and old, my beloved. In this way permit me to explain Isaiah, showing that he was not only a prophet, but an evangelist and an apostle as well. For he says about himself and the other evangelists: How beautiful are the feet of those who preach good news, of those who announce peace. And God speaks to him as if he were an apostle: Whom shall I send, who will go to my people? And he answers: Here I am; send me.
No one should think that I mean to explain the entire subject matter of this great book of Scripture in one brief sermon, since it contains all the mysteries of the Lord. It prophesies that Emmanuel is to be born of a virgin and accomplish marvellous works and signs. It predicts his death, burial and resurrection from the dead as the Saviour of all men. I need say nothing about the natural sciences, ethics and logic. Whatever is proper to holy Scripture, whatever can be expressed in human language and understood by the human mind, is contained in the book of Isaiah. Of these mysteries the author himself testifies when he writes: You will be given a vision of all things, like words in a sealed scroll. When they give the writings to a wise man, they will say: Read this. And he will reply: I cannot, for it is sealed. And when the scroll is given to an uneducated man and he is told: Read this, he will reply: I do not know how to read.
Should this argument appear weak to anyone, let him listen to the Apostle: Let two or three prophets speak, and let others interpret; if, however, a revelation should come to one of those who are seated there, let the first one be quiet. How can they be silent, since it depends on the Spirit who speaks through his prophets whether they remain silent or speak? If they understood what they were saying, all things would be full of wisdom and knowledge. But it was not the air vibrating with the human voice that reached their ears , but rather it was God speaking within the soul of the prophets, just as another prophet says: It is an angel who spoke in me; and again, Crying out in our hearts, Abba, Father’, and I shall listen to what the Lord God says within me.
Ex Prólogo commentariórum sancti Hierónymi presbýteri in Isaíam prophétam (Nn. 1. 2: CCL 73, 1-3)