Leo and Piper are married. Now Phoebe and Cole are married. Poor Paige really feels like an unnecessary extra, but that doesn't stop her continuing her dislike and mistrust of Cole, which, unfortunately, nobody else seems to share. It's a pity that they didn't take her more seriously because it turns out that The Source has plans to impregnate Phoebe with the spawn of evil so that she will, almost literally, give birth to the "Charmed" version of Rosemary's Baby.
This was a very good episode, particularly in the area of foreshadowing for future events as there is quite a bit of very interesting television to come.