The 19th century Scottish writer Thomas Carlyle coined the phrase "natural supernaturalism," which has been used by later critics to describe how the Romantic poets, and especially Wordsworth, viewed the natural world as a spiritual realm. The idea is that Heaven comes down to earth and is viewed as part of the world. This poem illustrates the principle of natural supernaturalism. The daffodils are like angels and twinkling stars, and the "bliss" of heaven occurs in speaker’s imagination. He uses Christian ideas and images to make an ode to nature without any reference to God.
The "inward eye" is just a metaphor for the memory and has no spiritual connotations whatsoever.
The "inward eye" connects the speaker to a spiritual reality of universal forms.