Identity as performance
No character in the play has a stable, honest identity. Jack is Ernest in London and Jack in the country. Algernon is himself in London and Ernest in Hertfordshire. Wilde shows that identity is something people construct for their audience, not something they simply have.
Marriage as a social transaction
Marriage in the play has almost nothing to do with love and everything to do with name, money, and social position. Lady Bracknell's interview of Jack makes this explicit. The women's fixation on the name Ernest shows it from another angle.
The absurdity of Victorian moral codes
The play treats Victorian seriousness as a target. Every character who performs virtue is hiding something. Wilde shows that the moral codes Victorians enforced publicly had almost no connection to how people actually lived privately.
Deception as a rational strategy
Algernon calls his system of lies Bunburyism and defends it as practical. The play does not punish either man for lying. Instead, their deceptions accidentally produce the truth. Wilde treats dishonesty as a reasonable response to an unreasonable society.
Class and social gatekeeping
Lady Bracknell represents a society that treats class origin as destiny. She refuses Jack not because he is a bad person but because he has no traceable family. The play resolves this by giving Jack an aristocratic origin, which Wilde presents as both a happy ending and a satirical joke about what society actually values.