The speaker of "The Lie" is dying. He wants to deliver a final message to all those who are considered "the best" in the world and commands his soul and, by extension, this poem to condemn various entities. The speaker's soul is commanded to visit the court, the church, heads of state, the zealous, and others and judge them all as liars.
Rhyme is central to this meaning because it, too, is a lie. Each stanza seems to follow an ababcc rhyme pattern; however, upon closer inspection, numerous pairs of words structured within this rhyme pattern are slant rhymes. The rhyme isn't exact and is only an illusion. Consider these pairs of words that are meant to rhyme in the established structural pattern:
Undercutting these words that don't exactly rhyme is the steadiness found in the repetition of each stanza's closure: "the lie." The lie is therefore dependable and predictable. The rhyme pattern, which is often slant and not exact, therefore creates a sense of disjointedness and falsehood, which contributes to the overall theme of deception in the poem.