Explain the voice of Iago in act 1 scene 3. lines 426-447
Do you mean the soliloquy that begins thusly? My line numbers are different...
In Iago's soliloquy, he confirms what we already know: he is a villain; he hates Othello; he is racist and sexist. Iago gives a reason why he hates Othello: "that 'twixt my sheetsHe has done my office," that he suspects Othello for sleeping with Emilia. This seems contrived, a byproduct of jealousy and misogyny. He offers no support or proof that Othello or Emilia have cheated; rather, he seems to be saying this to convince himself further to enact revenge on the Moor.
Iago lost Act I convincingly by playing the race card. Even though he doesn't speak in court to the Duke (he uses Brabantio as a mouthpiece), he has underestimated Othello and Desdemona's public defense: the Duke condones and blesses the marriage, even bestows further titles on Othello.
In this soliloquy, Iago is looking forward to Cyprus, where Othello and Desdemona will not have the Duke's allegiances, where law and order will give way to chaos. Iago will use sexism and jealousy to snare Othello. He will use Roderigo's money to finance his plan. He is a double-knave; he will look honest publicly and gain Othello's trust by convincing the general of Cassio's weaknesses (drinking). Iago will then work privately with lies to destroy Roderigo, Othello, Desdemona, even his own wife Emilia.
Overall, Iago's voice is similar to that of the Devil's (he will seduce with lies, play upon jealousy) and a Bastard's (a fatherless, dispossessed son who is jealous of his half-brother [Othello]). His language is beautiful and seductive (he has more lines in the play than Othello), and he seems resilient to enact revenge for no other purpose than sheer destruction.