15 In Jesus Christ, Son of God made Man, there shone the plentitude of divine revelation. "God, who at sundry times and in divers manners, spoke in times past to the fathers by the prophets last of all, in these days hath spoken to us by His Son" ( Heb . i. 1). The sacred books of the Old Testament are exclusively the word of God, and constitute a substantial part of his revelation; they are penetrated by a subdued light, harmonizing with the slow development of revelation, the dawn of the bright day of the redemption. As should be expected in historical and didactic books, they reflect in many particulars the imperfection, the weakness and sinfulness of man. But side by side with innumerable touches of greatness and nobleness, they also record the story of the chosen people, bearers of the Revelation and the Promise, repeatedly straying from God and turning to the world. Eyes not blinded by prejudice or passion will see in this prevarication, as reported by the Biblical history, the luminous splendor of the divine light revealing the saving plan which finally triumphs over every fault and sin. It is precisely in the twilight of this background that one perceives the striking perspective of the divine tutorship of salvation, as it warms, admonishes, strikes, raises and beautifies its elect. Nothing but ignorance and pride could blind one to the treasures hoarded in the Old Testament.
Source: Mit Brennender Sorge (Vatican.va)