A conceit is an extended metaphor. A metaphor is a comparison of two dissimilar things without using like or as. Bearing this in mind, Edward Taylor is using the image of a wasp chilled and unmoving from the cold to talk about the condition of the human soul when it is without God's grace, light, and love. The wasp warms itself in the sun until it can fly home, just as humans bask in God's love until they are ready to return home to their Creator. Taylor goes on to ask for the ability to clear his soul so that he too, like the wasp, might warm himself in the light of God until he is able to praise and take flight to his maker.
Edward Taylor typically wrote two kinds of poems: theological poems meant to evangelize, and more private, self-reflective poems. "Upon a Wasp Chilled with Cold" appears to be one of these more self-reflective poems, perhaps born out of Taylor's meditations on and observations of nature.
The previous response mentioned the poem's central ideas as being the condition of the human soul without God's love and the ways that God's love can revive. Another central idea is the speaker's fascination with the wasp's seemingly miraculous abilities to heal herself, which the speaker attributes to God, and the idea of hope even in the midst of the most dire struggles. Taylor writes, "As if her satin jacket hot / Contained apothecary’s shop / Of nature’s receipts, that prevails / To remedy all her sad ails, / As if her velvet helmet high / Did turret rationality." Thus, this little creature contains within her some powerful source of knowledge and healing (like a miniature apothecary's shop).
Taylor tells us that the wasp's miraculous inner powers of healing must come from God. The fact that God will help even the tiniest wasp, and the fact that the wasp is able to heal herself, gives the speaker a great deal of hope. Even "this little downy wasp" with a "small corporation" can teach us humans so many things, as she is "A nimble spirit who bravely mind / Her work in every limb." Taylor also seems to find hope in the fact that if God creates this little creature to have so much inner fortitude, then, with God, surely we, too, can discover our inner fortitude and heal ourselves.