In Othello, what reasons does Iago give for continuing to follow his master?In Act I, scene i of Othello.

Iago is in military service under Othello.  He is,
technically, his "ancient," which is a corruption of the word, "ensign."  In Elizabethan
English, this meant " href="http://www.tfd.com/ensign">standard-bearer"--an important distinction
since Iago has to carry Othello's identifying flag with his shield and colors and
represent him.

Why is this important?  The military
hierarchy and where Iago fits into it seems to have something to do with Iago's hatred
of Othello, who is not his "master," but rather his commanding officer and the one he
publically represents.  He does say:

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I follow him to serve my turn upon
him.

We cannot all be masters, nor all
masters

Cannot be truly
follow'd.

But continues
with:

In
following him, I follow but
myself.

So, though it bears
some similarities to a master/servant relationship, the "following" that Iago is doing
is in a military system in which both Othello and, more recently, Cassio are above him
in rank.

As for reasons, his reasons are evasive and not
direct, like the quote given above.  He follows Othello, but follows himself.  Not a
very clear statement. At the end of the scene he
says:

Though
I do hate him, as I do hell's pains,

Yet, for necessity of
present life,

I must show out a flag and sign of
love,

Which is indeed but a
sign.

So, it could be deduced
that he follows him to keep his job and keep food on the table ("for necessity of
present life").

Yet, it may not be useful to look too
closely at what Iago says about why he is doing anything.  He warns Roderigo (and the
audience) about his nature in line 64.  He says, "I am not what I am."  Though Iago
seems to give reason that it is necessary, at present, for him to follow Othello, it is
also hard to believe anything he says.  What Iago's reasons are for anything he does is
a question that has been debated over and over again through the
centuries.