Christian Doubt and the Source of Assurance
In a biblical view of knowledge, God’s word is the ultimate criterion of certainty. What God says must be true; for, as the letter to the Hebrews says, it is impossible for God to lie (Hebrews 6:18; compare Titus 1:2 and 1st John 2:27). His Word is Truth (John 17:17; compare Psalms 33:4, 119:160). So God’s Word is the criterion by which we can measure all other sources of knowledge.
When God promised Abraham a multitude of descendants and an inheritance in the land of Canaan, many things might have caused him to doubt. He reached the age of one hundred without having any children, and his wife Sarah was far beyond the normal age of childbearing. And though he sojourned in the land of Canaan, he didn’t own title to any land there at all. But Paul says of Abraham that “no distrust made him waver concerning the promise of God, but he grew strong in his faith as he gave glory to God, fully convinced that God was able to do what he had promised” (Romans 4:20-21). God’s Word, for Abraham, took precedence over all other evidence in forming his own belief. So important is this principle that Paul defines justifying faith in terms of it: “That is why [Abraham’s] faith was counted to him for righteousness” (verse 22).
Thus, Abraham stands in contrast to Eve, who (in Genesis 3:6) allowed the evidence of her eyes to take precedence over the command of God. Abraham is one of the heroes of the faith, who (according to Hebrews 11:13), “died in faith, not having received the things promised, but having seen them and greeted them from afar…” They had God’s promise, and that was enough to motivate them to endure terrible sufferings and deprivations through their earthly lives.
I would conclude that it is the responsibility of the Christian to regard God’s word as absolutely certain, and to make that word the criterion of all other sources of knowledge. Our certainty of the truth of God comes ultimately, not through rational demonstration or empirical verification, useful as these may often be, but from the authority of God’s own Word.