Metaphysical poetry involves the elevation of a seemingly common item or action to an almost spiritual level of importance, and John Donne’s “The Flea” illustrates this definition perfectly.
In the poem, the speaker equates the “two bloods mingled” within the body of a flea with the marriage of a man and his wife. Thus, the speaker argues to his lover that they, from a certain perspective, are “one blood made of two.” From the speaker’s perspective, the engorged flea is elevated from a pest to a “marriage bed” and “marriage temple.” The speaker seemingly transfers the sacred characteristics, meanings, and implications of marriage to a common flea.
However, the speaker does not stop with this argument. To reinforce his point, the speaker also warns his lover to not kill the flea because to do so would be “self murder.” By killing the flea, one would be destroying a part of the speaker and his lover as well as their “union.” Thus, the value of the flea is elevated to that of a human life as well.
The entire poem is driven by one comprehensive 'metaphysical conceit' and that is organized around this tiny and trifling object of the insect. It bites both the beloved and the lover and just because in its body, the blood of the two unite, the failed lover tries to convince his unwilling and indifferent beloved that the body of the flea is like their marriage bed where the love is already consummated.
Under the circumstances rather than killing the little flea and doing a crime, it is better for her to respect its unifying function and accept him as her lover.
Apart from the far-fethed and conceitful use of the flea symbolism, all its effects like---the tone of ironic wit, a satirical undercutting of romantic love, the argumentative structure of the poem, the combination of levity and seriousness--all these things make Donne's The Flea, a remarkable and representative Metaphysical poem.