What are the reasons that Othello believes Iago's accusations and insinuations about Desdemona? Elaborate with the reference to the text.

Othello believes Iago to be an honest, noble man. As a leader, Othello is uncertain in his role and consistently tries to prove himself because of the color of his skin, which leaves him open to maniplation. Othello is also a jealous man, something that Iago uses to his own advantage.

Oh, beware, my lord, of jealousy!
It is the green-eyed monster which doth mock
The meat it feeds on. (III.iii.)

Trifles light as air
Are to the jealous confirmations strong
As proofs of holy writ. (III.iii.)

But jealous souls will not be answered so.
They are not ever jealous for the cause,
But jealous for they’re jealous. It is a monster
Begot upon itself, born on itself. (III.iv.)