Jealousy as a weapon
Iago does not feel jealousy accidentally. He manufactures it in Othello on purpose, feeding him suspicion in controlled doses. The play shows jealousy as something that can be installed in a person by someone who knows their weak points. Once it takes hold in Othello, it overrides everything else he knows about Desdemona.
Race and outsider status
Othello is a Black man in a white Venetian world. He is respected as a general but treated as an exotic outsider in personal contexts. Iago and Brabantio both use racial language to undermine him. His outsider status makes him more vulnerable to the idea that Desdemona could not truly love him, which is exactly the crack Iago exploits.
Appearance versus reality
Iago is called honest by nearly everyone in the play. He is the most dishonest person in it. Othello believes what he is shown rather than what he knows. The play repeatedly shows characters acting on false information and missing the truth that is right in front of them.
The destruction of trust
Othello and Desdemona's relationship depends on trust, and Iago destroys it systematically. Once Othello starts doubting Desdemona, nothing she says or does can reassure him because Iago has framed every innocent action as suspicious. The play shows how hard trust is to rebuild once someone has decided to question it.
Gender and powerlessness
Desdemona, Emilia, and Bianca are all controlled by the men around them and suffer for it. Desdemona cannot defend herself against an accusation she does not understand. Emilia is silenced by Iago and then killed when she speaks up. The play puts women in positions where the truth they know cannot protect them.