They flash upon that inward eyeWhich is the bliss of solitude; (lines 21-22)
The daffodils have become a memory, but one that returns with full,
vivid force at strange moments, like when the speaker is just sitting
around, bored, with nothing in his head. It’s as if the images of
daffodils fill an empty space where thoughts should be ("vacant"), or
they push out other thoughts when there are too many ("pensive").
And then my heart with pleasure fills,And dances with the daffodils. (lines 23-24)
The spontaneous and unexpected return of the daffodils to his "inner
eye" brings the speaker back to the day he first saw them. Music and
dancing are the ultimate expressions of joy in the present moment, but
he can rediscover these joys even in his memory.