The first principle of sacred theology is divine revelation
V. The first principle of sacred theology, then, is divine revelation. By it every doubt about religion ends in the mind of a person who is truly Christian, watchful, and through the Holy Spirit earnestly wrestling with his own errors and sins. In that revelation his faith — the faith that makes him a Christian — at last conquers, stands, and is founded. It frees the assenting mind from every fear and suspicion of being deceived, and makes him so sure that he would rather suffer anything than deny what he has once embraced.
The Apostle calls this first principle of theological teaching the illumination of knowledge — φωτισμὸς τῆς γνώσεως (2 Corinthians 4:6–2 Corinthians 4:7): For God, who said light should shine out of darkness, has shone in our hearts to give the light of the knowledge of the glory of God in the face of Jesus Christ. But we have this treasure in earthen vessels, so that the surpassing power may be God's and not from us. Compare 1 Corinthians 2:4 and 1 Corinthians 2:13, where sacred analytics are set out for us, and a spiritual, efficacious demonstration is preferred uniquely to the persuasive words of human wisdom.
Latin
V. Est igitur primum sacrae Theologiae principium divina revelatio, qua omnis de religione dubitatio in animo hominis vere Christiani vigilantis & per Spiritum sanctum cum erroribus & peccatis suis serio luctantis, terminatur, & in qua fides ejus, a qua Christianus est, ita tandem vincit, subsistit ac fundatur, ut animum assentientis ab omni metu ac suspicione deceptionis liberet, & usque adeo certum reddat, ut malit tandem quidvis pati, quam quod semel amplexus est, abnegare. Primum principium tractationis theologicae Apostolo dicitur φωτισμὸς τῆς γνώσεως 2. Cor. 4. 6. 7. Quoniam Deus, qui dixit ut e tenebris lux splendesceret, qui splenduit in cordibus nostris, ad lumen cognitionis in facie Jesu Christi. Habemus autem thesaurum in testaceis vasculis, ut ejus virtutis praestantia sit Dei, & non ex nobis. Confer 1. Cor. 2. 4. 13. ubi analytica sacra nobis describuntur, adeoque demonstratio spiritualis & efficax prae πειθοῖς ἀνθρωπίνης σοφίας λόγοις unice commendatur.