62. The sensus fidei fidelis also enables individual believers to perceive any disharmony, incoherence, or contradiction between
a teaching or practice and the authentic Christian faith by which they live. They react as a music lover does to false notes in the performance of a piece of music. In such cases, believers
interiorly resist the teachings or practices concerned and do not accept them or participate in them. ‘The habitus of faith possesses a capacity whereby, thanks to it, the believer is
prevented from giving assent to what is contrary to the faith, just as chastity gives protection with regard to whatever is contrary to chastity.’
63. Alerted by their sensus fidei, individual believers may deny assent even to the teaching of legitimate pastors if they do
not recognise in that teaching the voice of Christ, the Good Shepherd. ‘The sheep follow [the Good Shepherd] because they know his voice. They will not follow a stranger, but they will run away from
him because they do not know the voice of strangers’ (Jn 10:4-5). For St Thomas, a believer, even without theological competence, can and even must resist, by virtue of the sensus fidei, his
or her bishop if the latter preaches heterodoxy. In such a case, the believer does not treat himself or herself as the ultimate criterion of the truth of faith, but rather, faced with materially
‘authorised’ preaching which he or she finds troubling, without being able to explain exactly why, defers assent and appeals interiorly to the superior authority of the universal Church.
74. In matters of faith the baptised cannot be passive. They have received the Spirit and are endowed as members of the body of the Lord
with gifts and charisms ‘for the renewal and building up of the Church’, so the magisterium has to be attentive to the sensus fidelium, the living voice of the people of God. Not only do
they have the right to be heard, but their reaction to what is proposed as belonging to the faith of the Apostles must be taken very seriously, because it is by the Church as a whole that the
apostolic faith is borne in the power of the Spirit. The magisterium does not have sole responsibility for it. The magisterium should therefore refer to the sense of faith of the Church as a whole.
The sensus fidelium can be an important factor in the development of doctrine, and it follows that the magisterium needs means by which to consult the faithful.
75. The connection between the sensus fidelium and the magisterium is particularly to be found in the liturgy. The faithful are
baptised into a royal priesthood, exercised principally in the Eucharist, and the bishops are the ‘high priests’ who preside at the Eucharist, regularly exercising there their teaching office, also.
The Eucharist is the source and summit of the life of the Church; it is there especially that the faithful and their pastors interact, as one body for one purpose, namely to give praise and glory to
God. The Eucharist shapes and forms the sensus fidelium and contributes greatly to the formulation and refinement of verbal expressions of the faith, because it is there that the teaching of
bishops and councils is ultimately ‘received’ by the faithful. From early Christian times, the Eucharist underpinned the formulation of the Church’s doctrine because there most of all was the mystery
of faith encountered and celebrated, and the bishops who presided at the Eucharist of their local churches among their faithful people were those who gathered in councils to determine how best to
express the faith in words and formulas: lex orandi, lex credendi.