From the beginning, Christians have been troubled by the question, “Which is more important: faith or works?” If you do good works, but have no faith, will that save you? Or if you believe in the Gospel, but do nothing to demonstrate your faith in action, will you be saved?
James asks, “What good is it, my brothers and sisters, if someone claims to have faith, but has no deeds? Can such a faith save them?” (James 2: 14) He then gives the example of going up to a poor person without decent clothes or food and saying, “Go in peace; keep warm and well fed.” What good do those good wishes do, if the person saying them does nothing to help? (v 16) But Paul says of Abraham's faith, “For this reason it depends on faith, in order that the promise may rest on grace. . .” (Romans 4: 16), and further that we are justified by faith. (Romans 5: 1) It sounds like these passages are contradicting each other.
But it is important to realize that faith, as Paul sees it, is not a passive mental activity only. Faith, for Paul, is an active virtue, like courage or prudence. It is not something that we just feel, it is something that causes us to act. Saying or thinking we believe in the promise of salvation means nothing to Paul, because it costs nothing; it is just a form of words. For faith to be a virtue, it must move us to action. Because we have faith in Christ, His death and resurrection and His promises, we act in a different way, we think a different way, we become a different person.
Mental assent to the Gospel is a necessary but not a sufficient step. We must start out by accepting the Gospel as true: that Jesus is in fact the Son of God, that He was crucified, and that He rose from the dead. We must also accept that these facts permit us to change our relationship to God, to become a child of God, as Jesus is. We must mentally assent to these propositions, as we do to the axioms of Euclid in plain geometry. As a student cannot make any progress in understanding geometry until he understands and accepts the axioms as true, so a potential Christian cannot reach the Gospel message and promise until he accepts the truth of Christ's death and resurrection.
But a student who accepts the axioms as true and then does nothing with them will not learn geometry. Only when the student begins to use the axioms to construct proofs does he begin to understand their deep truth and value. Only then does that student begin to be a geometer.
So it is with the Gospel. We cannot begin to become Christians until we accept as true the basic facts of Jesus's death and resurrection. But that is not enough; as James says, “Even the demons believe that—and shudder.” (James 2: 19b) Only when the believer begins to try to work out in his own life what the implications of the Gospel are, and begins trying to make those implications real in his life, does he become a Christian. If you believe that Jesus was a holy man who live a long time ago and said some interesting things, you will not be saved. If you believe that Jesus was a holy man who called people to repentance for their evil ways, and was killed for it, you will not be saved. Even if you believe that Jesus rose from the dead, you may not be saved. It is when you begin to see that Jesus's rising from the dead has changed the whole relationship between human beings and God, and that change puts imperative requirements on you, that you are saved.
God has shown, over and over in both the Old and New Testaments, that He is willing to give everyone the benefit of the doubt. His grace constantly overflows; David, the murderous adulterer, is forgiven. Peter, the coward at the most important moment in the Gospel story, is forgiven. Thomas the doubter is forgiven. Paul, the merciless persecutor is forgiven. And He, who looks at all His creation with love, will forgive those who give only mental assent to Christ. But He will not be satisfied with that. He demands that mental assent become action. For He does not save us as minds or spirits only.
As Presbyterians, we frequently say the Apostle's Creed, and blithely end it with, “I believe in . . . the resurrection of the body, and the life everlasting.” But if we really believe that (not just mentally assent to it as a proposition of faith), it must inevitably make a radical difference in our conduct. A person who will live forever in a physical body must have a very different outlook on life from a person who believes he will live eighty years or so and disappear forever, or even from a person who believes his soul may live on, but in another body with another identity.
God has eternity to work on us. One of the insights in mathematics is that half of infinity is still infinity, and a millionth of infinity is still infinity—even the smallest fraction of infinity is still infinite. God will use infinity to lead us from purely mental assent to a real change in the kind of person we are, if we will let Him. Or we can insist on saying no forever. Purely mental assent is enough at the beginning. But it will not be enough at the end.
Paul says, “If I give away all I have, and if I deliver up my body to be burned, but have not love, I gain nothing.” (I Corinthians 13: 3) Rational assent to God's power, and a rational calculation that if we make sacrifices for others we are pleasing God, will not save us. God is not taken in by the Cartesian bargain. As Jesus said, "Thus, when you give to the needy, sound no trumpet before you, as the hypocrites do in the synagogues and in the streets, that they may be praised by others. Truly, I say to you, they have received their reward.” (Matthew 6: 2) God is not satisfied by rational calculation only. Either we believe and have faith, and that faith forces us to change the way we treat our fellow human beings, or we are trying to fool God.
We are saved by our faith. Our faith forces us to see our fellow human beings in a different way, as beloved children of God, just as we are. That insight forces us to treat others differently. That way of looking at God's children causes us to do God's work, not because we are trying to bribe God, but because we really care about others, as God cares about them. So our faith is proved by our works, both in the modern sense of “providing convincing arguments for, (Euclidean proof)” and in the older sense of “testing the truth of (proving ground).” We believe, and we care—and God, who sees all as it really is, but cares for all as they try to be, takes all we try for, and makes us His children.