Regarding the phrase churches of God,
it is common for Paul to designate Christian communities in a particular place as belonging to God (1 Corinthians 1:2; 1 Corinthians 10:32; 1 Corinthians 11:16, 1 Corinthians 11:22; 1 Corinthians 15:9; 2 Corinthians 1:1; Galatians 1:13; 2 Thessalonians 1:4; 1 Timothy 3:5). This designation distinguishes the Christian assembly (church
= ἐκκλησία/ekklesia) from other assemblies—such as a city's citizen assembly—for which the word ἐκκλησία/ekklesia was also used. It also draws attention to the privilege of belonging to God.1
14 For you, brothers, became imitators of the churches of God in Christ Jesus that are in Judea. For you suffered the same things from your own countrymen as they did from the Jews,