How may it appear that the writings of the Prophets and Apostles were indicted of God?
Partly by testimonies, partly by reason. And the testimonies, partly inward, partly outward. The internal witness is one alone; namely of the holy Ghost inwardly speaking to our heart, and persuading us that those writings are inspired of God, and sealing them up in our hearts, Eph. 1:13; 1 John 2:20, 27, Ye have an anointment of the Lord, and this anointment teaching you all things. For whosoever are led by the Spirit of God, can easily discern his power speaking in the Scriptures. As it is said, 1 Cor. 2:15, The spiritual man discerneth all things, and Isa. 53:1, The arm of the Lord is not revealed to all men. So, Luke 8:10 and Mark 13:11, The mysteries of the kingdom of heaven are not revealed to all men, but to whom it is given of God. And this testimony properly maketh for our confirmation, and this alone doth satisfy us, being known of them alone that are converted unto Christ, which doth evermore agree with the Scripture, without which the testimony of the Church can be no weight with us. For as none but God alone is a fit witness to testify of himself in his word, even so the word never findeth credit in our hearts, till such time as it be sealed up unto us by the inward testimony of the Spirit.*
*Note the continuity of Bucanus’ commentary with that of the Westminster Confession of Faith, 1647, Ch. 1.5., “yet notwithstanding, our full persuasion and assurance of the infallible truth and divine authority thereof, is from the inward testimony of the Holy Spirit bearing witness with and by the Word in our hearts,” and John Calvin in his Institutes written in 1559, “[But] I reply, that the testimony of the Spirit is superior to all reason. For as God alone is sufficient witness to himself in his own word, so also the word will never gain credit in the hearts of men, till it be confirmed by the internal testimony of the Spirit. It is necessary, therefore, that the same Spirit, who spake by the mouths of the prophets, should penetrate into our hearts, to convince us that they faithfully delivered the oracles which were divinely entrusted to them…; because, till he illuminate their minds, they are perpetually fluctuating amidst a multitude of doubts.” Calvin, Institutes, 1.7.4. For a century, from 1559-1659 and indeed, before and after, Protestant orthodox theology recognized that it is the Holy Spirit through the Word that confirms the truth of Scripture to the faithful believer in Jesus Christ.
William Bucanus, Body of Divinity or Institutions of the Christian Religion; framed out of the Word of God, and the writings of the best divines, methodically handled by was of questions and answers, fit for all such as desire to know and practice the will of God. Written in Latin. Translated into English by Robert Hill and Fellow at St. Johns College in Cambridge, for the benefit of the English Nation. (London: Printed for Daniel Pakeman, Abel Roper and Richard Tomlins, and are to be sold in Fleet-street, and at the Sun and Bible near Py-corner, 1659), 45-46.