What is verbal plenary inspiration? How can we be sure the Bible is actually God speaking to us?
Verbal Plenary Inspiration
In short, verbal plenary inspiration is this; verbal means spoken verbally or in the written form. In the Bible it ends up being both since God spoke directly to some (i.e., Moses, Abraham, Isaiah, the Apostle John), while God had others moved by the Holy Spirit to write down what He wanted, but either way, God moved the author to write exactly what the Spirit of God intended to be in Scripture. This includes the Old Testament and New Testament or the present 66 books of the Bible. Any other books outside of these 66 books (called the Apocrypha) are not inspired by God. They might be inspiring, but they are not the words of God, so the spoken or written word is verbal. Plenary means full, complete, absolute, and unqualified which is what Scripture is. Of course, inspiration means just that; the author was inspired by the Spirit of God to record the Word of God, or what we have today as the Bible. Verbal plenary inspiration then is the spoken or written Word of God that is the complete, perfect, and unqualified Word of God. We know that it is inspired by the Holy Spirit Who is God. 
The Apostle Paul wanted Timothy to rely on Scripture alone as his principle teaching material. Of course, that’s wise because “All Scripture is breathed out by God and profitable for teaching, for reproof, for correction, and for training in righteousness” (2 Tim 3:16). The Scriptures are to be taught so “that the man of God may be complete, equipped for every good work” (2 Tim 3:17), and it is vital for Timothy (and us) to know “that no prophecy of Scripture comes from someone’s own interpretation” (2 Pet 1:20). These weren’t Paul’s words but the very words of God. Obviously the Apostle Paul knew that “no prophecy was ever produced by the will of man, but men spoke from God as they were carried along by the Holy Spirit” (2 Pet 1:21), and that included his own writings. God “spoke by the mouth of his holy prophets from of old” (Luke 1:70), but they were not the words of the prophets. They were the words of God spoken through the prophets. They were breathed out by God but written down by men. The word Paul uses in “breathed out” is literally “expiration” or “breathed outward,” so the breath of God is what is recorded in Scripture. Just like we use breath or breathed out when we speak words, God spoke or breathed out the words of Scripture to men. God’s Word is God’s breath or His breath speaking out to us through the written Word, the Bible.
The author of Hebrews wrote, “Long ago, at many times and in many ways, God spoke to our fathers by the prophets, but in these last days he has spoken to us by his Son, whom he appointed the heir of all things, through whom also he created the world” (Heb 1:1-2). Jesus still speaks to us, in these last days, but it is through His written Word. His words are found in the four gospels, so Jesus is still speaking to us today, and by means of His Spirit, making sense of them. The intended purpose of God’s Word was so we would “remember the predictions of the holy prophets and the commandment of the Lord and Savior through your apostles” (2 Pet 3:2) and take heart in that. In other words, what they prophesied came true because it was God speaking through them, and God is faithful to His Word and can bring to pass what He purposes. Not one of His precious promises will ever fail. They never have and they never will.
The “verbal” part of verbal plenary inspiration is just what it sounds like; it’s verbal. It is God speaking; either through the Holy Spirit which moved the authors to write, and Who opens up the Scriptures to us. It is sometimes verbal where God’s Word is spoken through teaching or preaching of the Word. In some cases, God actually spoke to the authors as He did Moses and Isaiah and they recorded those words, but verbal plenary inspiration only applies to the original manuscripts and not all the different kinds of translations. There are errors in almost every translation, but today we have better scholarship and have better assurance that what we read today in our Bible is about 99% of the pure, unadulterated Word of God. Most errors are grammatical in nature or where words are transposed, like “Jesus Christ” and “Christ Jesus.” Both are basically correct and neither order affects biblical doctrine, so any differences are less than 1% and those errors don’t affect the major teachings of the Christian faith.
What a privilege to have a Bible in our homes. We can read it with freedom and without fear of persecution or the threat of death. In many places around the world, the Bible is illegal and punishable by death, so many have taken the Bible apart and each person has memorized the different books of the Bible. I guess it’s easier to hide one book of the Bible than it is the whole Bible. These Christians then exchange their books of the Bible and memorize the one given to them. Truly, they’ve done what the psalmist recommends; they’ve hidden God’s Word in their hearts (Psalm 119:11). If the authorities ever find the books, they might destroy them, but they’ll never destroy what’s hidden in their hearts; the very breath of God inspired by God and hidden in the hearts of the children of God.
Here is some related reading for you: How Do We Know the Bible is True? Is it Really the Word of God? 
Resource – Scripture quotations are from The Holy Bible, English Standard Version® (ESV®), Crossway Bibles. (2007). ESV: Study Bible: English standard version. Wheaton, Ill: Crossway Bibles. Used by permission. All rights reserved.