The sensation of being in the company of your lover is second to nothing of which the speaker can conceive. Feelings takes precedence over anything that is of the nature of an intellectual construct, like syntax, wisdom, paragraphs, or marks of punctuation. The speaker links his feelings to blood, and to spring and flowers, all functions of nature, and thus superior to anything artificial that man can produce.
Wisdom is the accumulation of knowledge through experience and observation, and the speaker feels that it is overrated. To him, kisses are more elemental and profound, and the flutter of his lover's eyelids moves him more deeply than any thought he can form. He seems to believe that life is for living through the senses, through erotic interaction, because death is not a "parenthesis." The implied meaning is that death is a truth and inevitability. In injecting this note, cummings's speaker cements his argument that he and his lover must laugh and fall together in an embrace while they can.
In the poem, the speaker says kisses are better than wisdom and her eyelids’ flutter is better than the “best gesture" of his brain. Kisses and the flutter are expressions of emotion. They are not filtered by logic, wisdom or the formulaic structure of syntax, paragraphs and intellectualizing. The speaker is saying that emotional gestures are more spontaneous and therefore more sincere than a structured thought. He makes an analogy between the constraints of syntax and grammar on poetry with the constraints of wisdom on emotion. For emotion and/or poetry to be free and experienced to fullest, they must be free of these constraints, or as the speaker says:
who pays attention
to the syntax of things
will never wholly kiss you: