Fashion was very important in the Victorian world because it defined not only who you where, but what you where, both financially and socially.
The latest fashions were very expensive and only available to people who were rich and had standing in society. To persuade an acknowledged high quality couture to make a gown for you required not only money but a position in society. Then, as now, it did not follow that if you had money you were accepted into high society.
It was quite impossible to be accepted into a respectable club or to attend a social gathering unless you were correctly dressed. Last year's fashion quickly relegated one to a lower social structure. It was easy to see who was and who was not able to keep up with the Joneses, so to speak.
It was unusual, to say the lest for a person to be invited to private functions outside their families own class. Whilst there was a desire to improve ones social standing it was not done to mix with people above ones station in life other than in a business capacity.
Life in Victorian times took place on a number of different levels, one can almost say it occupied different worlds which could be defined in terms of breeding, etiquette, education and appearance. Ones appearance was the first and the most obvious of these things to be observed by a stranger, if you failed with this there was unlikely to be an opportunity to succeed with other attributes, as the social door would be closed unless you had gained the support of a patron.
In short your clothes defined you and the social, business and work group you would be assigned to.