But to them that are called (αυτοις δε τοις κλητοις). Dative case, to the called themselves.

Christ (Χριστον). Accusative case repeated, object of κηρυσσομεν, both the power of God (θεου δυναμιν) and the wisdom of God (θεου σοφιαν). No article, but made definite by the genitive. Christ crucified is God's answer to both Jew and Greek and the answer is understood by those with open minds.