Since the Reformation faith has been recognized to have three parts: knowledge, assent, and trust. Let's take a few minutes to dig into these three essential elements of faith.
To believe something we have to know something about the something. We cannot believe in a vacuum. Belief is based on information. Knowledge is that information. Someone has said that we believe based upon the sufficiency of evidence. Knowledge is that evidence.
If someone says, "I believe that Ben Carson is going to win the Republican nomination for president." For you to believe it you have to know something about Ben Carson. You have to know something about the political process of party nominations. You may want to know why the other person is confident that Ben Carson will win the nomination. To know this information may convince you of the same thing or maybe not, but the point is that to believe or not to believe you have to know things. That is what is meant by knowledge. To believe in Jesus as the eternal Son of God, that He is God Himself, that He died an atoning death for the sins of the world, that He calls you to believe who Scripture says He is, requires information. Without some information or knowledge you will not be able to believe. Because of the necessity of knowledge for faith it is called a "precondition" of faith.
Knowledge then is the first part of saving faith. This is Paul's point in Romans 10:14. How then will they call on him in whom they have not believed? And how are they to believe in him of whom they have never heard? And how are they to hear without someone preaching? (Rom. 10:14).
The knowledge upon which saving faith is based is ultimately the testimony of God. It is revealed knowledge. It is not reasoned. Mankind could never reason their way to the knowledge of the Gospel. As Peter confessed that Jesus is "the Christ, the Son of the living God" Jesus told him that flesh and blood has not revealed this to you, but my Father who is in heaven (Mt. 16:17). The knowledge of the Gospel is available because God reveals it. It is His testimony, and it is His character which undergirds His testimony (Tit. 1:2). Therefore to reject the knowledge of the Gospel is to call God a liar (1 Jn. 5:9-12).
Without knowledge faith is entirely subjective, "I 'feel' like I should believe." Or it is dependent upon a mystical experience, "I heard a voice tell me to believe." Only in these ways can we believe without knowledge. So without knowledge faith must be subjective or mystical.
Assent is agreement that something is true. Knowledge or evidence compels us to say I believe or not. Assent believes the evidence. Assent is necessary for a true faith. Theologian and philosopher Francis Schaeffer pointed out the obvious when he said, "There is only one reason to become a Christian and only one because it is true!" This is the work of assenting. It is affirming that the knowledge we have is true.
Yet, assent is not saving faith. James makes this point, You believe that God is one; you do well. Even the demons believe – and shudder! (2:19). The demons regularly confessed Jesus as the Messiah (e.g. Mt. 12:23; Mk. 1:24), but they did not become His followers. They continued to follow Satan knowing that the Judgment awaited them, and they shuddered. One can believe that something is true without it having any constraint upon his or her life. This is the inadequacy of assent, and why it falls short of saving faith. One can know who Jesus is, and he can assent or agree that that knowledge is true; and then walk away unaffected.
Saving faith has knowledge, assent, and, finally and most crucially, trust. Trust is referred to as "fiduciary". As such one entrusts to another something of value. In the faith that justifies one must trust the Redeemer to redeem. Charles Spurgeon described it this way, "Jesus is what he is said to be, Jesus will do what he says he will do; therefore we must each one trust him, saying, 'He will be to me what he says he is, and he will do to me what he has promised to do; I leave myself in the hands of him who is appointed to save, that he may save me. I rest upon his promise that he will do even as he has said.' This is a saving faith, and he that hath it hath everlasting life."1 Spurgeon went on to say, "Now, true faith in its very essence rests in this, - a leaning on Christ. It will not save me to know that Christ is a Saviour; but it will save me to trust him to be my Saviour. I shall not be delivered from the wrath to come, by believing that his atonement is sufficient; but I shall be saved, by making that atonement my trust, my refuge, and my all."2
Trust moves beyond mere assent. Trust is constrained by the conviction of the truth to surrender, to rest upon, to lean upon Jesus. Thus, trust has also been described as "commitment following from conviction," thereby living by the truth received. Therefore, trust can say with the Apostle Paul, I know whom I have believed, and I am convinced that he is able to guard until that Day what has been entrusted to me (2 Tim. 1:12). Only this kind of faith pleases God (Heb. 11:6).
Faith has three components: knowledge, assent, and trust. These make for a saving faith and a faith which pleases God. Knowledge alone is not enough. To know or understand something can still have zero influence. Further, one must assent or agree that the knowledge is true. Certainly we will not adhere to something if we believe it to be false. But believing something is true does not constrain us to do more than we are doing, or to do something different than we are doing. Until we can trust this knowledge personally, until we are convicted of the truth so that we trust in it we have not believed with a saving faith.
Spurgeon offers this pastoral concern:
My fear is lest the reader should rest content with understanding what is to be done, and yet never do it. Better the poorest real faith actually at work, than the best ideal of it left in the region of speculation. The great matter is to believe on the Lord Jesus at once. Never mind distinctions and definitions. A hungry man eats though he does not understand the composition of his food, the anatomy of his mouth, or the process of digestion: he lives because he eats. Another far more clever person understands thoroughly the science of nutrition; but if he does not eat he will die, with all his knowledge. There are, no doubt, many at this hour in hell who understood the doctrine of faith, but did not believe. On the other hand, not one who has trusted in the Lord Jesus has ever been cast out, though he may never have been able intelligently to define his faith. O dear reader, receive the Lord Jesus into your soul. And you shall live for ever. "He that believeth in Him hath everlasting life.3
1 Spurgeon, "What is Faith?," All of Grace, 48.
2 Spurgeon, "Faith," Spurgeon's Sermons, Vol. 1, 370.
3 Spurgeon, "What is Faith?," All of Grace, 49.