Pelikan seeks to show, with great erudition, that the Cappadocians were able to synthesize Hellenic concepts, not all theological in origin, to meet the needs of their baptism of Greek thought into that of a more or less unified Christian vision. Emphasis is placed upon their use of apophatic theology (talking of God by saying what God is not- negation).
Really a useful book to dispel the myths that the theology of the Church, especially the Greek tradition, is, a al Harnak, a big squabble over an iota or a bunch of clap trap that disguises the gospel. Each culture appropriates the Gospel in a manner that makes it intelligible. Of course there will be some loose ends and need of trimming, but Pelikan expertly demonstrates the genius of these theologians in their synthetic abilities.
My other reviews of theological books may be of interest to you in this regard. See The Mystical Theology of the Eastern Church for another refutation of the "Hellenization of Christianity" thesis. Moreover, see Light from the Christian East: An Introduction to the Orthodox Tradition for more on how the Christian tradition asked new questions apart from the Hellenistic context, and used some Hellenic concepts in a modified form to answer and articulate a new worldview.