The Old Testament books announced Mary

The books of the Old Testament describe the history of salvation, by which the coming of Christ into the world was slowly prepared. These earliest documents, as they are read in the Church and are understood in the light of a further and full revelation, bring the figure of the woman, Mother of the Redeemer, into a gradually brighter light. 

When it is looked at in this way, she is already prophetically foreshadowed in the promise of victory over the serpent, given to our first parents after their fall into sin (Gen 3:15). 

Likewise she is the Virgin who shall conceive and bear a son, whose name will be called Emmanuel (cf. Is. 7: 14;  Mic. 5: 2-3; Mt. 1: 22-23).

She stands out among the poor and humble of the Lord, who confidently hope for and receive salvation from Him. 

Finally, with her, the exalted Daughter of Sion, and after a long expectation of the promise, the times are fulfilled and the new Economy established, when the Son of God takes a human nature from her, that He might in the mysteries of His flesh free man from sin.

Lumen Gentium Chapter VIII, II. The Role of the Blessed Mother in the Economy of Salvation §55 - Vatican II Council