Here Calvin discusses the place of the Word of God and the role of the Holy Spirit when it comes to faith.
“And so, whether adversities reveal God’s wrath, or the conscience finds in itself the proof and ground thereof, thence unbelief obtains weapons and devices to overthrow faith. Yet these are always directed to this objective: that, thinking God to be against us and hostile to us, we should not hope for any help from him, and should fear him as if he were our deadly enemy.
“To bear these attacks faith arms itself with the Word of the Lord. And when any sort of temptation assails us – suggesting that God is our enemy because he is unfavourable towards us – faith, on the other hand, replies that while he afflicts us he is also merciful because his chastisement arises out of love rather than wrath. When one is stricken by the thought that God is Avenger of iniquities, faith sets over against this the fact that his pardon is ready for all iniquities whenever the sinner betakes himself to the Lord’s mercy. Thus the godly mind, however strange the ways in which it is vexed and troubled, finally surmounts all difficulties, and never allows itself to be deprived of assurance of divine mercy. Rather, all the contentions that try and weary it result in the certainty of this assurance.
“[…] But our mind has such an inclination to vanity that it can never cleave fast to the truth of God; and it has such a dullness that it is always blind to the light of God’s truth. Accordingly, without the illumination of the Holy Spirit, the Word can do nothing. From this, also, it is clear that faith is much higher than human understanding. And it will not be enough for the mind to be illumined by the Spirit of God unless the heart is also strengthened and supported by his power.
“[…] Indeed, the Word of God is like the sun, shining upon all those to whom it is proclaimed, but with no effect among the blind. Now, all of us are blind by nature in this respect. Accordingly, it cannot penetrate into our minds unless the Spirit, as the inner teacher, through his illumination makes entry for it.”
John Calvin, Institutes of the Christian Religion, III.2.20, 21, 33, 34
Calvin’s point is that while unbelief may often be fuelled by either external unpleasant circumstances or by internal subjective phenomena so that you begin to lose trust that God is for you and not against you, the antidote for this slide is the Word of God. Because although circumstances are ambiguous the promises of the God are clear; and so circumstances must be interpreted by the clear promises of Scripture. But because of our natural bent towards sin and unbelief and away from God and obedience to His Word, the Word of God by itself is of no advantage without the Holy Spirit at work in us and alongside it, changing and strengthening our hearts and illuminating the Word.