Poetry produces intensity from precision, parsimony, and sometimes rhyme. Forced rhyme compromises sincerity. Absent rhyme often signals self-obsessed ramblings of a feeble mind---unlike Updike's. Rhyme slipped nonchalantly---mid-sentence, mid-stanza---punctuates thought the way only the spoken word can, thus giving thoughts physical expression. Broken lines and split sentences are spurious pauses. They discourage the reader from racing through the seamless verse. A poem is akin to a music score; it must be spoken to be appreciated fully.
When one is receptive of confession, Updike's poetry infects one with the capacity for the thought-soaked feeling. The poems' intensity (the better ones', at any rate), however, prevents them from captivating a distracted mind. Prose, with its more nuanced intensity, is better at winning the reader's confidence and nurturing his pensive mood.