61. ‘Beloved, do not believe every spirit, but test the spirits to see whether they are from God ; for many false prophets have gone out into the world’ (1Jn 4:1). The sensus fidei fidelis confers on the believer the capacity to discern whether or not a teaching or practice is coherent with the true faith by which he or she already lives. If individual believers perceive or ‘sense’ that coherence, they spontaneously give their interior adherence to those teachings or engage personally in the practices, whether it is a matter of truths already explicitly taught or of truths not yet explicitly taught.
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.
64. The sensus fidei fidelis also enables the believer to distinguish in what is preached between what is essential for an authentic Catholic faith and what, without being formally against the faith, is only accidental or even indifferent with regard to the core of the faith. For example, by virtue of their sensus fidei, individual believers may relativise certain particular forms of Marian devotion precisely out of adherence to an authentic cult of the Virgin Mary. They might also distance themselves from preaching which unduly mixes together Christian faith and partisan political choices. By keeping the spirit of the believer focused in this way on what is essential to the faith, the sensus fidei fidelis guarantees an authentic Christian liberty (cf. Col 2:16-23), and contributes to a purification of faith.
65. Thanks to the sensus fidei fidelis and sustained by the supernatural prudence that the Spirit confers, the believer is able to sense, in new historical and cultural contexts, what might be the most appropriate ways in which to give an authentic witness to the truth of Jesus Christ, and moreover to act accordingly. The sensus fidei fidelis thus acquires a prospective dimension to the extent that, on the basis of the faith already lived, it enables the believer to anticipate a development or an explanation of Christian practice. Because of the reciprocal link between the practice of the faith and the understanding of its content, the sensus fidei fidelis contributes in this way to the emergence and illumination of aspects of the Catholic faith that were previously implicit; and because of the reciprocal link between the sensus fidei of the individual believer and the sensus fidei of the Church as such, that is the sensus fidei fidelium, such developments are never purely private, but always ecclesial. The faithful are always in relationship with one another, and with the magisterium and theologians, in the communion of the Church.
[(*) PRELIMINARY NOTE
In its quinquennium of 2009-2014, the International Theological Commission studied the nature of sensus fidei and its place in the life of the Church. ... The text “Sensus fidei in the Life of the Church” ... was then submitted to its President, Cardinal Gerhard L. Müller, Prefect of the Congregation for the Doctrine of the Faith, who authorized its publication.]