Idols and serving God

In chapter 9 Justin follows the traditional OT polemic against idol worship, adding that there is demonic inspiration behind such worship.

In contrast, the true God, who cannot be represented in any form, and has no personal name, is to be worshipped through the imitation of his "excellences", especially "temperance...justice...philanthropy."

Epistle to Diognetus

My next stopping stage in browsing through ancient sources is the "Epistle to Diognetus" . Written to someone who was not a Christian it seeks to demonstrate how Christians are different from pagans and Jews. Thus, chapter 2 provides a strong statement of the futility of idols, drawing on the Old Testament tradition of satire towards their existence.

Chapters 3 and 4 provide a critique of Judaism. Sacrifices, sabbath keeping, circumcision and festivals are particularly singled out for attention. What puzzles me at the moment is that these are all outlined in the Old Testament, and yet the author seems to suggest that they are unworthy for Christian worship.

Will the next chapters provide an answer to the riddle? Or does the author have an almost marcionite approach to the OT?