To True Religion is opposed, 1. Infidelity, in which case the name of Christian is not granted. For, although Infidelity might extend itself much further, and have a place even among those that with the mouth profess the Word of faith and also dwell in the external communion of the Church; indeed, in some measure even in the very faithful, complaining of their ὀλιγοπιστίᾳ, little faith,[1] and asking that the Lord might help their ἀπιστίᾳ/unbelief, Mark 9:24;[2] Luke 17:5: although also all heresy either openly rejects, or at least twists unto a perverse sense, one or many parts of Scripture through Infidelity/Unbelief; nevertheless, Infidelity/Unbelief κατ᾽ ἐξοχὴν, par excellence, is wont to be attributed to those that do not even receive the Christian name but are detested, Mohammedans, contemporary Jews, Pagans, who verily reject, not only all or the principal heads of Religion, but also the very principia, and do not admit the entire Sacred Scripture as the norm of faith. In which sense Paul speaks of ἀπίστοις/unbelievers and ἀπιστίᾳ/unbelief, 1 Corinthians 7:12-15; Romans 11:20.
[1] For example, Matthew 6:30: “Wherefore, if God so clothe the grass of the field, which to day is, and to morrow is cast into the oven, shall he not much more clothe you, O ye of little faith (ὀλιγόπιστοι)?”
[2] Mark 9:24: “And straightway the father of the child cried out, and said with tears, Lord, I believe; help thou mine unbelief (μου τῇ ἀπιστίᾳ).”