Franciscus Junius (1545-1602) was a Reformed scholar and theologian who studied under John Calvin and Theodore Beza at Geneva and later became professor at the universities of Heidelberg and Leiden. Below are excerpts from his posthumously published Opera Theologica, in which he states that the testimony of the Holy Spirit is the ultimate assurance of the divinity, inspiration and authority of Scripture.
Junius distinguishes between a testimonium internum and a testimonium externum for the authority of Scripture:
“The testimonies are either internal or external. The internal testimony that exceeds all other authority and without which all the other testimonies and arguments will be of no weight or importance for us, is the Holy Spirit speaking to our hearts and testifying to our spirits that these books of Holy Scripture are θεοπνευστος (God-breathed), that is, dictated by Him.”
– Franciscus Junius (1545-1602), Opera Theologica 1, Opuscula Theologica Selecta 117-118
Junius then states that the external testimony is threefold: The first external testimony is Scripture itself or rather God who speaks to us in Scripture and asserts its divine authority. The second is the testimony of the prophets and apostles who have handed over to the church what they received from the Lord. The third is the witness of the church that gives a constant and perpetual consent to Scripture. This third externum testimonium is restricted. Just as Scripture is canonical and authentic in itself (in se), it also appears to be so to us (nobis), and the testimonium of the church is mute and invalid without the testimony of the Spirit. The internal testimonium not only persuades believers that everything in the Scriptures is dictated by God, but also enables them to discern these books from the counterfeit books by a spiritual judgment. After the testimonies Junius mentions eleven arguments from which the authority of the Scriptures also can be concluded. Among these are some of Calvin’s arguments, such as the heavenliness of its doctrine, the unity of its parts, and its antiquity. But he says:
“Although all these arguments bind and force our judgment and strongly prove that Scripture is truly divine, still they absolutely cannot persuade us firmly of this, unless the testimonium of the Holy Spirit comes with them. That alone gives these arguments power and not only forces and presses us, like them, but also awakens our whole mind to assent and fills our hearts with wonderful assurance (πληροφορια) and causes us to embrace Holy Scripture as truly θεοπνευστος (God-breathed).”
– Franciscus Junius (1545-1602), Opera Theologica 1, Opuscula Theologica Selecta 118
What is said of the arguments can be applied to the external testimonies as well: only the Holy Spirit can give us the full assurance of the divine origin and authority of Scripture.