It's one of the few parts of the Book that is crystal clear.
The warnings are to the seven existing churches.
Some people allegorize them, but they are seven actual
churches at the time of John's writing.

There may be a deeper meaning, as much of prophecy is
type and shadow of the future.

In addition, they hold warnings that are applicable to
all churches of all times.

If they are symbolic of seven church ages "literally"
I've never seen a convincing delineation of it.

Our present time is frequently compared to the Laodicean
church, but you can see that church all throughout
church history, or the descriptions of it.