Faith is Heb 11:1 “the assurance of things hoped for, the conviction of things not seen,” our firm belief in God and all that He has revealed to us through Holy Mother Church. 1 Thes 2:13 “When you received the word of God which you heard from us, you accepted it not as the word of men but as what it really is, the word of God.”
Faith resides in our intellect; we believe because God is all-knowing (cannot be deceived) and all-good (cannot deceive), so what He tells us is infallibly true. Our faith must be constant; the apostle Thomas gave Jesus three years of faithful service, but we remember him for his one moment of doubt.
Our faith must be complete. We completely submit our intellect and will to God. Our faith therefore illuminates our daily life. Our fallen race inherits from its first parents a propensity to sin, but our constant objective must be to live as Holy Mother Church teaches. We seek to live by the theological and cardinal virtues. We consciously avoid the seven capital sins. We go to the Holy Sacrifice of the Mass every day if possible, or every Sunday at minimum. We go to Confession every week if possible, or every month at minimum. We do all this because we have faith that the Catholic Church has Christ’s authority to teach us how to prepare for heaven.
Our faith is a free assent to the whole truth that God has revealed. We have faith only if we believe in Christ’s entire public revelation. The Catholic faith is faith that Christ instituted a divine institution, a Church blessed with authority to infallibly teach His public revelation. If we accept only doctrines consistent with our own experience we are not accepting them on faith but rather on human analysis.
The virtue of faith is also one of the twelve fruits of the Holy Spirit.
For a discussion of faith in the context of “faith and works” see justification.
Vatican documents on Faith, Revelation and the Bible.