There was a reason Ra was so confident this time around, even if Lex couldn't see it yet. With his left eye, he observed the fallen deity, and though he discovered certain weaknesses, most were beyond his current ability. Purity was an obvious weakness, but it would not work as well against Ra as it did his minions. Pure divine energy, ironically, seemed to be a weakness as well.
Besides that, Lex also looked out for its strengths. Lex was sure that Ra knew that his minions could never hope to defeat him, but he sent them forth, anyway. Perhaps he wanted to use the black sludge coming out of their bodies to poison him somehow, or maybe they were just a part of a greater setup. If Lex could determine the deities plan beforehand, he could work against it.
Unfortunately, he could learn nothing of note. That left him only one option - to defeat Ra before he could pull whatever trick he had in mind.
