This short but potent book is an explanation and apologetic of the doctrine of the substituionary atonement of Jesus Christ. It does a good job of being accessible and simultaneously profound.
As Sproul points out, "the words crucial and crux both have their root in the Latin word for 'cross,' crux, and they have come into the English language with their current meanings because the concept of the cross is at the very center and core of Biblical Christianity."
There's a lot packed into this little book. I recommend it to anyone interested in deepening their understanding of the necessity, meaning, and implications of the cross of Christ, from the new believer to the seminary student.