A Faith Fortified by the Word of God
In Book Third, Chapter 2, Section 21, John Calvin gives a fuller explanation of the nature of a persevering faith.
To withstand these assaults, faith arms and fortifies itself with the word of God. … Thus the pious mind, how much soever it may be agitated and torn, at length rises superior to all difficulties, and allows not its confidence in the divine mercy to be destroyed. No, rather, the disputes which exercise and disturb it tend to establish this confidence.
… Therefore, as we have already said, we again maintain, that faith remaining fixed in the believer’s breast never can be eradicated from it. However it may seem shaken and bent in this direction or in that, its flame is never so completely quenched so as to not at least to lurk under the embers. In this way, it appears that the word, which is an incorruptible seed, produces fruit similar to itself. Its germ never withers away utterly and perishes. The saints cannot have a stronger ground for despair that to feel, that, according to present appearances, the hand of God is armed for their destruction; and yet Job thus declares the strength of his confidence: “Though he slay me, yet will I trust in him.”
The truth is, that unbelief reigns not in the hearts of believers, but only assails them from without; does not wound them mortally with its darts, but annoys them, or, at the utmost, gives them a wound which can be healed. Faith, as Paul declares (Eph 6:16), is our shield, which receiving these darts, either ward them off entirely, or at least breaks their force, and prevents them from reaching the vitals. Hence when faith is shaken, it is just as when, by the violent blow of a javelin, a soldier standing firm is forced to step back and yield only a little; and again when faith is wounded, it is as if the shield were pierced, but not perforated by the blow. The pious mind will always rise, and be able to say with David, “Yea, though I walk through the valley of the shadow of death, I will fear no evil: for thou art with me” (Ps 23:4). Doubtless it is a terrific thing to walk in the darkness of death, and it is impossible for believers, however great their strength may be, not to shudder at it; but since the prevailing thought is that God is present and providing for their safety, the feeling of security overcomes that fear.
As Augustine says, whatever be the engines which the devil erects against us, as he cannot gain the heart where faith dwells, he is cast out. Thus if we may judge by the event, not only do believers come off safe from every contest, so as to be ready, after a short repose, to descend again into the arena, but the saying of John, in his epistle, is fulfilled, “This is the victory that overcometh the world, even our faith” (1 John 5:4). It is not said that it will be victorious in a single fight, or a few, or some one assault, but that it will be victorious over the whole world, though it should be a thousand times assailed.