We also learn that Iago is a very experienced soldier (or at least he believes himself to be).
Iago's contempt of Othello, and also his role in the army, is brought to the fore in line 29 where he says his Moorship's ancient' this being said with a great amount of sneering and contempt. The fact that Iago refers to Othello as a Moor' and his Moorship' goes further in showing us how Iago dislikes Othello (as opposed to addressing him as Othello). It also shows that Iago believes that Negro are racially unequal.
Iago feels a binding that forces him to be loyal to Othello as we find out in line 36 where he says Whether I in any just term am affined To love the Moor. We also discover that Roderigo hates Othello to with By heaven, I rather would have been his hangman' (when Roderigo says his' he is referring to Othello).
Iago is biding his time in the demise of Othello as can be obtained from I follow him to serve my turn upon him' telling us that Iago is patient in his waiting for revenge. He feels that if he continues to be servile he will be discarded, we discover this from That, doting on his own obsequious bondage, Wears out his time, much like his master's ass, For naught but provender; and when he's old cashiered.
Iago also believes that those who pay respect to others for their own advancement, once they have gained their ends can follow their own inclinations openly. Refer to Do themselves homage.
We suddenly discover that Iago's true nature is not what he portrays outwardly I am not what I am', this is a very important clue to Iago's true nature, what exactly is not revealed to us (not just yet). .
Roderigo immediately throws a deliberate offensive comment regarding Othello with thick-lips'. The Elizabethans didn't make any distinction between Moor and Negro but as was said before Roderigo is being deliberately offensive here.
Something suddenly sparks in Iago's mind and his riotous imagination is let loose.