There are several passages that express well Paul’s “theology of the cross.” I’ll quote three here:
For the Jews demand signs and Greeks seek wisdom, but we preach Christ crucified, a stumbling block to jews and folly to Gentiles, but to those who are called, both Jews and gentiles, Christ the power of God and the wisdom of God. I Corinthians 1:22-24
For I decided to know nothing among you except Jesus Christ and him crucified. I Corinthians 2:2
For in him all the fulness of God was pleased to dwell, and through him to reconcile to himself all things, whether on earth or in heaven, making peace by the blood of his cross. Colossians 1:20
Some other notable passages are Galatians 6:14-15, Ephesians 2:16, Colossians 2:14, and I Corinthians 1:18. The theme of the cross is central to Paul’s letters. First because it makes common to Jews and gentiles alike the core of Jesus mission – our redemption through his death and resurrection. Secondly, Paul affirms the extraordinary historical reality that Jesus of Nazareth was crucified, and that, indeed, he rose from the dead.
Paul’s theology of the cross is so common in his letters that some historians argue that it was St. Paul who popularized the idea that Jesus of Nazareth rose from the dead – whether or not it was actually true. Knowing nothing of Scripture, this peanut gallery overlooks the fact that Jesus death and resurrection is fairly central to other books of the New testament – Acts and the Gospel of John, for instance. Furthermore, neither Acts nor John shows any literary or theological Pauline influence.
But Paul should be credited with being the first Christian writer who, outside of the Gospels, independently proposes a “theology of the cross.” This is the belief that redemption and salvation was won “on the cross” through Jesus Christ. It is a position held universally by all Christians, and it is so obvious that “redemption through Christ’s Passion” has never been debated among Christians.
This is not to say that there are different, and competing developments of Paul’s theology. Martin Luther suggested that the cross was “all sufficient.” By this he meant that Christ’s death and resurrection was the last word on salvation, and that no act or good work on our part could merit or “add to” our own salvation when it was already won by Christ. Catholics, Orthodox and many high-church Protestants do not accept this position without qualification.
Another disputed interpretation of Paul’s theology of the cross suggests that Christ not only redeems humankind, but that he will save all of humankind (meaning everyone, including those in hell) at the final judgment, as a result of his death and resurrection. This theology was proposed by Origen of Alexandria, and then rejected by the Second Council of Constantinople. Recently, the theologians Hans Urs Von Balthasar and Karl Rahner have re-considered the possibility that a) hell is unpopulated and b) Christ intends, and ultimately will, save all of humankind – through the cross.
While Christians can debate whether the cross is “all sufficient,” or whether Christ indeed will spare all of humankind from damnation, we are all in agreement that His resurrection is an historical reality, and through his death and resurrection he redeemed the world.