Faith is the theological virtue by which we believe in God and believe all that he has said and revealed to us, and that Holy Church proposes for our belief, because he is truth itself. By faith, "man freely commits his entire self to God." For this reason, the believer seeks to know and do God's will. "The righteous shall live by faith." Living faith "work(s) through charity." CCC 1814
The theological virtues have God himself as their origin, motive and direct object. Infused with sanctifying grace, they bestow on one the capacity to live in a relationship with the Trinity. They are the foundation and the energizing force of the Christian’s moral activity and they give life to the human virtues. They are the pledge of the presence and action of the Holy Spirit in the faculties of the human being. (#384)
The virtue of faith is a gift in "which we believe in God and believe all that he has said and revealed to us" and we fully commit ourselves to do His will. This is a living faith, not intellectual assent alone, but instead "faith working through love" (Gal 5:6) because as Scripture testifies, "faith apart from works is dead" (Jas 2:26).
The Catechism Companion, Vol II has some good commentary on this:
We have faith in God. We hope in God, regardless of where life leads us. We love him. Unless we have faith, there is always going to be a skeptic that lives inside us. But when we have encountered the living God and hear what he reveals, our questions come not from cynicism or skepticism but from wanting to understand... Faith requires action. We are saved by grace - God's free gift - through faith working itself out in love. (p. 248)