Rohmer likes his morals and the moral for me here is how moving from one stage in life to another can't be forced. We can't decide to be in a different 'place' in life on a whim, without doing the maturing first. There's no short-cut.
The cringeworthy party scene is perhaps the telling scene. Not just because of Sabine's inability to crawl out from childish ways, but equally Edmond's inability to cast his mind back to a time when he was giddy and foolish and work didn't matter.
The supporting cast - friend Claude, Mother and the antiques dealer all have wisdom that comes through experience, but they know better than to waste too much breath with logic that headstrong Sabine is not ready for.
A rites of passage, "find-out-the-hard-way" movie that's not as slight as first glances might suggest.