Notice the opposites Cummings uses.
A person who pays attention to the “syntax of things” (lines 2–3) is contrasted with someone who is “wholly…a fool” (line 5). What opposites does he pose to wisdom (line 9), the brain (line 11), and life (line 15)?
As you say, the poet is setting up a number of things that he says are opposites.
In line 9, he speaks of wisdom. In this case, the opposite of wisdom is given in the previous line, line 8. He says that the opposite of wisdom is kisses and kisses are better than wisdom.
When he talks about his brain, it is a "gesture" of his brain. It is contrasted to the "flutter" of the listener's eyelids.
Finally, you ask about the opposite of life. The opposite of life seems to be a paragraph. You can argue that it's death, but I think it's a paragraph because he is saying that life is no paragraph and so it seems he's contrasting life with that rather than with death.