Faith rests on God's truthfulness; certainty resolves into the Spirit's secret testimony
We have taught that religion's dogmas, and other things handed down by God's word, can carry many arguments for their truth. Those arguments are still not the proper and principal reason on which the faith rests that receives what God's word hands down. That reason is rather the authority and truthfulness of God as he teaches and reveals.
God's word itself — divine revelation — does have notes and marks by which it can be recognized and told apart from diabolical and human frauds. Even so, our faith does not rest chiefly on notes and marks of that kind. Its certainty is resolved into the Holy Spirit's secret testimony, and into that inward efficiency by which he immediately makes the faithful certain it is God who speaks, and presses a firm persuasion of this on our minds.
Latin
IV. Docuimus, licet religionis dogmata, et alia quae verbo Dei traduntur, multa argumenta suae veritatis habere possint, tamen argumenta ista non esse propriam et praecipuam rationem cui innititur fides qua res Dei verbo traditas accipimus; sed potius authoritatem et veracitatem Dei docentis et revelantis. Ipsum vero Dei verbum, seu divinam revelationem, habere quidem notas et indicia, quibus internosci possit, et a diabolicis et humanis fraudibus distingui, nihilominus fidem nostram non niti potissimum hujuscemodi notis et indiciis: sed certitudinem illius resolvi in arcanum Spiritus S. testimonium, et internam illam efficientiam, qua fideles certos reddit immediate Deum esse qui loquitur, et firmam hac de re persuasionem mentibus nostris imprimit.