The infallibility of Scripture simply means that the word of God cannot err. Not only is Scripture inerrant- does not contain errors or contradictions- but it cannot and is incapable of failing to communicate God's predetermined truth. In other words, the Bible will not fail in its purpose to reveal the One True God and his amazing plan of salvation to undeserving sinners. The word of God is indefectible. The Bible will not deceive or mislead anyone who trusts the God who both declared its words and had them written and preserved.
This is a very important doctrine. After all, Scripture is at the center of the Christian life. We are saved by hearing the word of God, the gospel, proclaimed and the Spirit making God's words effectual in our souls. We are sanctified by studying and hearing the word of God and the Spirit convicting and conforming us more into the image of Christ our Lord. We are comforted by the words of God. We pray the words of God. We sing the word of God. We feed upon the word of God. It is the word of God that guides, sustains, encourages, satisfies, reveals, heals, shepherds, warns, protects, and teaches. What kind of God gives us a word that cannot be trusted? Can't God preserve his word? Would God allow errors within his holy, inspired, inerrant word? Of course not! God is completely trustworthy. His word can be trusted and obeyed. The doctrines of Scripture cannot be divorced from one another. They build upon each other. Because Scripture is inspired, it is inerrant. Since Scripture is inerrant, it is also infallible. You do not have one without the others. If one of these truths is removed, the entire structure crumbles- the word of God could not be trusted. But, praise God! The Bible is inspired, inerrant, and infallible.
The word of God cannot err for two reasons. First, God cannot lie. If the Bible is the word of God and God cannot lie, then it follows that the Bible will not contain any errors, misinform, or misdirect. “God is not man, that he should lie, or a son of man, that he should change his mind. Has he said, and will he not do it? Or has he spoken, and will he not fulfill it?” (Num. 23:19) “Paul, a servant of God and an apostle of Jesus Christ, for the sake of the faith of God's elect and their knowledge of the truth, which accords with godliness, in hope of eternal life, which God, who never lies, promised before the ages began...” (Tit. 1:1-2) “ So when God desired to show more convincingly to the heirs of the promise the unchangeable character of his purpose, he guaranteed it with an oath, so that by two unchangeable things, in which it is impossible for God to lie, we who have fled for refuge might have strong encouragement to hold fast to the hope set before us.” (Heb. 6:17-18)
Second, God is not ignorant of anything. Errors come from imperfections and ignorance. God is perfect and not encumbered by any of these. God knows all things perfectly. Hence, his word can be trusted because it cannot err. “Great is our Lord, and abundant in power; his understanding is beyond measure.” (Ps. 147:5) “And no creature is hidden from his sight, but all are naked and exposed to the eyes of him to whom we must give account.” (Heb. 4:13) “God is greater than our heart, and he knows everything.” (1Jn. 3:20)
The word of God is true because God is truth. Truth is without errors and mistakes. God does not make mistakes. His word is exactly what he desires mankind to have.
God is true. “ By no means! Let God be true though every one were a liar, as it is written, 'That you may be justified in your words, and prevail when you are judged.'” (Rom. 3:4) “Against you, you only, have I sinned and done what is evil in your sight, so that you may be justified in your words and blameless in your judgment.” (Ps. 51:4) “And this is eternal life, that they know you the only true God, and Jesus Christ whom you have sent.” (Jn. 17:3)
God's word is the word of truth. “And take not the word of truth utterly out of my mouth, for my hope is in your rules.” (Ps. 119:43) “The sum of your word is truth, and every one of your righteous rules endures forever.” (Ps. 119:160) “ Sanctify them in the truth; your word is truth.” (Jn. 17:17)
God's law is truth. “Your righteousness is righteous forever, and your law is true.” (Ps. 119:142) “But you are near, O LORD, and all your commandments are true.” (Ps. 119:151) “The law of the LORD is perfect, reviving the soul; the testimony of the LORD is sure, making wise the simple; the precepts of the LORD are right, rejoicing the heart; the commandment of the LORD is pure, enlightening the eyes; the fear of the LORD is clean, enduring forever; the rules of the LORD are true, and righteous altogether. More to be desired are they than gold, even much fine gold; sweeter also than honey and drippings of the honeycomb. Moreover, by them is your servant warned; in keeping them there is great reward.” (Ps. 19:7-11)