One of the compliments non parents often say about new parents is that "having a baby hasn't changed them". They mean it nicely - they mean you can still talk about things other than babies, that you manage to go to the occasional party, that you are still the kind of person they want to be friends with - but they are wrong. Becoming a parent does change you, absolutely and entirely.
It's not just that your responsibilities and priorities change, though they do. It's that something changes your very being to the core.
The experience of having a baby changes you physiologically and emotionally. You carry the weight of responsibility for another person, and a responsibility towards society to do a good job bringing up that person. But more than that, it changes your identity. However good or bad a job you do of it, the answer to whether or not you are a parent irreversibly changes and with it the way other people look at you and judge you and analyse who your are.
Your personality may stay the same, you may (if you are lucky) look the same. You may do the same job and read the same books and laugh at the same jokes, but fundamentally and profoundly who you are has changed. You are a different person. You are a parent and with that comes all the judgements and responsibilities we associate with that word as well as a sense of complete untouchability, for though you are vulnerable now in a way you have not been before you are also untouchable, for as long as your child is okay you know you will be okay.
So when people say "you haven't changed" it's not really a compliment, but it also cannot possibly be true. You have changed, utterly and completely, and so you should.
Related post: My baby, my daemon