Clearly this poem is centrally about the need for fantasy in our lives and how opening the door and letting Fancy free is something that can add great joy and happiness to our personal conditions. In addition, Fancy is so important to have in our lives because the real and personal pleasures that we all enjoy are actually only fleeting and swiftly leave us just as they swiftly arrive. Note how the poem begins, which also acts as something of a refrain in the poem as a whole:

Ever let the Fancy roam,
Pleasure never is at home:
At a touch sweet Pleasure melteth,
Like to bubbles when rain pelteth;
Then let winged Fancy wander
Through the thought still spread beyond her:
Open wide the mind's cage-door,
She'll dart forth, and cloudward soar.

The poem then is based around the relationship between fantasy, or "Fancy," and our personal lives as we release Fancy so that we can experience more lasting pleasures than the temporary and ephemeral pleasures that our lives bestow us with. According to the poem therefore, resorting to Fancy or fantasy is a necessary action due to the way that "Pleasure never is at home" and the overwhelming need that we have as humans for something more to brighten up our existence. Fantasy and the personal are thus intermingled in this poem through our need for Fancy in our lives.