"At this point I would like to sketch a path intended to help us understand more profoundly not only the content of the faith, but also the act by which we choose to entrust ourselves fully to God, in complete freedom. In fact, there exists a profound unity between the act by which we believe and the content to which we give our assent. Saint Paul helps us to enter into this reality when he writes: “Man believes with his heart and so is justified, and he confesses with his lips and so is saved” (Rom 10:10). The heart indicates that the first act by which one comes to faith is God’s gift and the action of grace which acts and transforms the person deep within.
The example of Lydia is particularly eloquent in this regard. Saint Luke recounts that, while he was at Philippi, Paul went on the Sabbath to proclaim the Gospel to some women; among them was Lydia and “the Lord opened her heart to give heed to what was said by Paul” (Acts 16:14). There is an important meaning contained within this expression. Saint Luke teaches that knowing the content to be believed is not sufficient unless the heart, the authentic sacred space within the person, is opened by grace that allows the eyes to see below the surface and to understand that what has been proclaimed is the word of God.
Confessing with the lips indicates in turn that faith implies public testimony and commitment. A Christian may never think of belief as a private act. Faith is choosing to stand with the Lord so as to live with him. This “standing with him” points towards an understanding of the reasons for believing. Faith, precisely because it is a free act, also demands social responsibility for what one believes. The Church on the day of Pentecost demonstrates with utter clarity this public dimension of believing and proclaiming one’s faith fearlessly to every person. It is the gift of the Holy Spirit that makes us fit for mission and strengthens our witness, making it frank and courageous.
Profession of faith is an act both personal and communitarian. It is the Church that is the primary subject of faith. In the faith of the Christian community, each individual receives baptism, an effective sign of entry into the people of believers in order to obtain salvation. As we read in the Catechism of the Catholic Church: “ ‘I believe’ is the faith of the Church professed personally by each believer, principally during baptism. ‘We believe’ is the faith of the Church confessed by the bishops assembled in council or more generally by the liturgical assembly of believers. ‘I believe’ is also the Church, our mother, responding to God by faith as she teaches us to say both ‘I believe’ and ‘we believe’.”"
~ Pope Benedict XVI
PORTA FIDEI
(w2.vatican.va)