Ὅμηρον ἐξ Ὁμήρου σαφηνίζειν → explain Homer from Homer, explain Homer with Homer

[spiros]

Ὅμηρον ἐξ Ὁμήρου σαφηνίζειν → explain Homer with Homer

[bailongma]

Ὅμηρον -- Homer, accusative
ἐξ Ὁμήρου -- from Homer
σαφηνίζειν -- infinitive, to make clear ("explain"; σαφη here comes from the adj. "clear")

thus: "to explain Homer from Homer"