Saving faith involves content. We are not justified by believing just anything. Some have said, “It doesn’t matter what you believe as long as you are sincere.” That sentiment is radically opposed to the teaching of the Bible. The Bible teaches that it matters profoundly what we believe. Justification is not by sincerity alone. We may be sincerely wrong. Right doctrine, at least in the essential truths of the gospel, is a necessary ingredient of saving faith. We believe in the gospel, in the person and work of Christ. That is integral to saving faith. If our doctrine is heretical in the essentials, we will not be saved. If, for example, we say we believe in Christ but deny His deity, we do not possess the faith that justifies.
Though it is necessary to have a correct understanding of the essential truths of the gospel in order to be saved, a correct understanding of them is not enough to be saved. A student can earn an A on a Christian theology exam, grasping the truths of Christianity, without himself affirming that they are true. Saving faith includes the mind’s assent to the truth of the gospel.
R. C. Sproul, Essential Truths of the Christian Faith (Wheaton, IL: Tyndale House, 1992).