1. Replacing apocalyptic enthusiasm for the parousia with "salvation-history".
2. Legitimizing the identity of Christian Gentiles (a favourite these days).
3. Reconciling Pauline and Petrine Christianities.
4. An apology for the Apostle Paul.
5. To evangelize Jews of the Diaspora.
6. To extol the virtues of the Christian community as worthy of imitation.