The Church of Smyrna refers to the persecuted church and myrrh which releases it fragrance by being crushed.
The church age that it represents refers to the second and third centuries, where the church of Jesus Christ was violently persecuted by Roman dictators.
Jesus commends this church for its faithfulness in extreme tribulation and poverty. [Similar to how the church in China stays faithful and wins millions of souls despite persecution from the Communist Chinese Government].