To the angel of
the church of Ephesus write,
‘These things says He who holds the seven stars in His right hand, who walks in the midst of the seven golden lampstands:
Revelation 2:1
To
the church of God which is at Corinth, to those who are sanctified in Christ Jesus, called to be saints, with all who in every place call on the name of Jesus Christ our Lord, both theirs and ours:
1 Corinthians 1:2
when Paul writes to a city he refers to "the church" in that city.
When Paul wrote to a region with many large cities he addressed the churches.
Paul, an apostle (not from men nor through man, but through Jesus Christ and God the Father who raised Him from the dead), and all the brethren who are with me, to
the churches of Galatia:
Galatians 1:2
Where in this post did I say Paul wrote the book of Revelation?