Can we content ourselves with such an unreal faith in Christ, as in no sufficient measure includes self abasement, or thankfulness, or the desire or effort to be holy? For how can we feel our need of his help, or our dependence on him, or our debt to him, or the nature of his gift to us, unless we know ourselves? How can we in any sense be said to have that “mind of Christ,” to which the Apostle exhorts us, if we cannot follow him to the height above, or the depth beneath; if we do not in some measure discern the cause and the meaning of his sorrows….
Obedience to God’s commandments, which implies knowledge of sin and holiness, and the desire and endeavour to please him, this is the only practical interpreter of Scripture doctrine. Without self-knowledge you have no root yourselves personally; you may endure for a time, but under affliction or persecution your faith will not last. This is why many in this age (and in every age) become infidels, heretics, schismatics, disloyal despisers of the Church. They cast off the form of truth, because it never has been to them more than a form. They endure not, because they never have tasted that the Lord is gracious; and they never have had experience of his power and love, because they have never known their own weakness and need.
Blessed John Henry Newman