Ephesus was a leading city where Paul ministered for years and where a strong church grew. In Revelation, the risen Christ commends the Ephesians' hard work but warns them: thou hast left thy first love.
Ephesus stands as a caution to every church and believer — that faithfulness in activity can still lose the warmth of devotion it began with.
Ephesus in Scripture
Nevertheless I have somewhat against thee, because thou hast left thy first love.