Recently, the doctrine of penal substitution has come under heavy attack from certain Evangelicals (notably Brian McLaren in the US and Steve Chalke in Britain). Liberal Protestants have been attacking it for over a century now, but for those calling themselves Evangelicals to do it is a new development and one which portends significant changes in the years ahead for the Evangelical movement as it grapples with this innovation.
One of the ways Evangelicals have tried to straddle the fence on this issue is to argue that downplaying (or even denying) the logic of penal substitution (and sometimes of substitution of any kind) without losing an objective doctrine of the atonement is to emphasize the doctrine of Christus Victor. But, clearly, not all versions of Christus Victor are actually objective; this doctrine can (and often is) be deployed in a subjective manner that makes it into a kind of example of victory that inspires us to fight all the harder to defeat the powers too.
Justin Taylor, at his blog Between Two Worlds (which is now hosted at the Gospel Coalition site) has written a succinct and lucid explanation of how Christus Victor is related to penal substitution. He points out that Col. 2:14-15 says specifically that Christ triumphed over the principalities and powers by his cross. (Note: an objective Christus Victor doctrine must emphasize the death and not merly the resurrection of Christ.) Taylor quotes John Murray to the effect that redemption from sin cannot be conceived properly except as it comprehends Christ's victory over Satan and the powers. The victory of Christ over sin, death, hell and the Devil has always been an integral part of the orthodox doctrine of the atonement.
But then Taylor asks the excellent question of how exactly this victory is attained and and in what sense is it attained specifically through the cross? He quotes George Smeaton, a 19th century professor of exegetical theology at Edinburgh who provides the answer:
"Sin was (1) the ground of Satan’s dominion, (2) the sphere of his power, and (3) the secret of his strength; and no sooner was the guilt lying on us extinguished, than his throne was undermined, as Jesus Himself said (John 12:31). When the guilt of sin was abolished, Satan’s dominion over God’s people was ended; for the ground of his authority was the law which had been violated, and the guilt which had been incurred. . . .
[A]ll the mistakes have arisen from not perceiving with sufficient clearness how the triumph could be celebrated on His cross. (The Apostles’ Doctrine of the Atonement (Edinburgh, T. & T. Clark, 1870), 307–308; my emphasis and numbering)."
So Christus Victor is based on, and effective only because of, the sin-bearing work of Christ on the cross. Penal substutution is necessary for a doctrine of Christus Victor to have an application to the real world; without it Christus Victor is just pie in the sky or, at most, an inspiring myth designed to encourage us to try a little harder. But trying harder is not what the Gospel is about; the Gospel is the sublime announcement that despite the fact that all our striving is in vain, God in Christ has already accomplished salvation for all who believe. This makes Christus Victor good news.
So J. I. Packer is right; penal substitution is the heart of the Gospel and the heart of the doctrine of the atonement. As the heart, it is not the whole of the organism, but it is the part that pumps the blood to the whole organism thus keeping it alive and healthy. If the Church ceases to preach penal substitution, the whole significance of Christ's work will wither and dry up leaving only moralism, works righteousness and the social gospel in the place where a full-orbed Gospel used to be.