In an older post, "Testing God," Gideon, and Praying about the Book of Mormon, I discussed how the incident of Gideon asking God for a sign in Judg 6:36-40, a request God grants him, refutes the common claim that LDS request people to pray about the Book of Mormon, as per Moroni 10:3-5, is blasphemous as one is "testing God."
The following from the book of Exodus further supports this. In the following text, Yahweh provides a number of signs for Moses to give to the people to prove the truthfulness of his prophetic calling:
And Moses answered and said, But, behold, they will not believe me, nor hearken unto my voice: for they will say, The Lord hath not appeared unto thee. And the Lord said unto him, What is that in thine hand? And he said, A rod. And he said, Cast it on the ground. And he cast it on the ground. And he cast it on the ground, and it became a serpent; and Moses fled from before it. And the Lord said unto Moses, Put forth thine hand, and take it by the tail. And he put forth his hand, and caught it, and it became a rod in his hand that they may believe that the Lord God of their fathers, the God of Abraham, the God of Isaac, and the God of Jacob, hath appeared unto thee. And the Lord said furthermore unto him, Put thine hand into thy bosom. And he put his hand into his bosom: and when he took it out, behold, his hand was leprous was snow. And he said, Put thine hand into thy bosom again. And he put his hand into his bosom again; and plucked it out of his bosom, and, behold, it was turned again as his other flesh. And it shall come to pass, if they will not believe thee, neither hearken to the voice of the first sign, that they will believe the voice of the latter sign. And it shall come to pass, if they will not believe also these two signs, neither hearken unto thy voice, that thou shalt take of the water of the river and pour it upon the dry land: and the water which thou takest out of the river shall become blood upon the dry land. (Exo 4:1-9)
Protestants who level this charge also conveniently overlook how essential the "internal witness of the Holy Spirit" is to their epistemology. Consider the following:
We may be moved and induced by the testimony of the Church to an high and reverent esteem of the Holy Scripture. And the heavenliness of the matter, the efficacy of the doctrine, the majesty of the style, the consent of all the parts, the scope of the whole (which is, to give all glory to God), the full discovery it makes of the only way of man's salvation, the many other incomparable excellencies, and the entire perfection thereof, are arguments whereby it does abundantly evidence itself to be the Word of God: yet notwithstanding, our full persuasion and assurance of the infallible truth and divine authority thereof, is from the inward work of the Holy Spirit bearing witness by and with the Word in our hearts. (Westminster Confession of Faith, Chapter 1: "Of the Holy Scripture" [emphasis added])
In the Second Helvetic Confession, from 1566, under chapter 1, “Of the Holy Scripture Being the True Word of God,” we read the following in section 5:
Neither do we think that therefore the outward reaching is to be thought as fruitless because the instruction in true religion depends on the inward illumination of the Spirit, or because it is written ‘No man shall teach his neighbor; for all men shall know me’ (Jer. xxxi. 34), and ‘he that watereth, or he that planteth, is nothing, but God that giveth the increase’ (1 Cor. iii. 7). For albeit ‘no man can come to Christ, unless he be drawn by the Heavenly Father’ (John vi. 44), and be inwardly lightened by the Holy Spirit, yet we know undoubtedly that it is the will of God that his word should be preached even outwardly. God could indeed, by his Holy Spirit, or by the ministry of an angel, without the ministry of St. Peter, have taught Cornelius in the Acts; but, nevertheless, he refers him to Peter, of whom the angel speaking says, ‘He shall tell thee what thou oughtest to do’ (Acts x. 6) (Philip Schaff, The Creeds of Christendom, vol. III: The Evangelical Protestant Creeds [revised by David S. Schaff; New York: Harper and Row, 1931; repr., Grand Rapids, Mich.: Baker Books, 2007], 832; emphasis added)
Norman Geisler, a leading Protestant apologist and philosopher, and his co-author Ralph MacKenzie, wrote the following on how they, as Protestants, "know" the Bible to be true:
Reformed theologians also believe that the Spirit of God brings divine assurance that the Bible is the Word of God. This is known as the witness of the Spirit. Only the God of the word can bring full assurance that the Bible is the Word of God.. Further, Reformed theologians acknowledge that aid of the Holy Spirit in understanding and applying the Scriptures to our lives. But he does not do this contrary to the Bible or contrary to good rules of biblical interpretation. (Norman Geisler and Ralph MacKenzie, Roman Catholics and Evangelicals: Agreements and Differences [Grand Rapids, Mich.: Baker, 1995], 179 n. 6)
Similarly, in a recent book-length defense of Sola Scriptura, God's Word Alone: The Authority of Scripture (Grand Rapids, Mich.: Zondervan, 2016), Matthew Barrett wrote the following:
Calvin was clear that the Scripture’s credibility does not depend on man’s reason but on the testimony of the Holy Spirit. Calvin explains that we will never be persuaded of the trustworthiness and authority of Scripture’s doctrine until we are “persuaded beyond doubt that God is its Author.” Therefore, the “highest proof of Scripture derives in general from the fact that God in person speaks to it.” In that light, we must look to a “higher place than human reasons, judgments, or conjectures” and turn instead to the “secret testimony of the Spirit.” The “Word will not find acceptance in men’s hearts before it is sealed by the inward testimony of the Spirit.” The same Spirit who spoke through the prophets will penetrate “into our hearts to persuade us that they faithfully proclaimed what had been divinely commanded” (Institutes of the Christian Religion 1.7.4). (p. 67)
Many of the “contradictions” that scholars found problematic a century ago have now been resolved with time and study. Nor can we neglect the role of the Spirit. What at first appears to be an unsurmountable hurdle later becomes a small speed bump when the Spirit illuminates the Word so that we can better understand its meaning. (p. 266)
[I]nternal clarity is quite different [to external clarify]. Because the unbeliever is spiritually blind, he cannot see the truth of Scripture in a saving way unless his eyes are opened by the Holy Spirit (Luther, Bondage of the Will, in LW 33.28 [cf. 98-99]). So while a person may read and memorize the Scriptures backward and forward, exegete its words, diagram its sentences in the original languages, and masterfully describe the historical and cultural background of an individual text, this is not to say that the person has truly understood Scripture’s message. There is knowing Scripture, and then there is knowing Scripture. The latter is work of the Holy Spirit. (p. 320)
Sufficiency does not preclude the inward illumination of the Holy Spirit. While we should not be seeking revelation from the Spirit in addition to Scripture, we must not go to the other extreme (as some evangelical rationalists have done) and eliminate the Spirit entirely. Rather, Word and Spirit go together. God gives us his sufficient Word, but he intends the Spirit to come alongside us to help us understand his Word. Therefore, must like Calvin (see chapter 1), the Westminster Confession advocates the illuminating work of the Spirit: “The Spirit . . . [is] necessary for the saving understanding of such things as are revealed in the Word (John 6:45; 1 Cor. 2:9-12).” (p. 337)
Scripture reassures us that should we come to God’s Word with the Spirit as our counselor, the Lord will reward our hungry soul with sweet and satisfying food (1 John 2:20, 26-27). (p. 344)
I cannot prove the Bible is true. Only the Spirit can do that. And until he does, you will never see Scripture as God’s Word . . . The Bible testifies to its own identity. But this isn’t enough. We must then pray that the Spirit would irresistibly persuade sinners that the Bible is what it says it is. (p. 374)
As with so many of their charges against Latter-day Saint theology and Scripture, Evangelical critics are guilty of engaging in eisegesis of Scripture and blatant double-standards.
