Paul's letters were not only to the church of Corinth at that time, they were also to "all that in every place call upon the name of Jesus Christ our Lord".
1Cor 1:1-2 Paul, called to be an apostle of JesusChrist through the will of God, and Sosthenes our brother, Unto the church of God which is at Corinth, to them that are sanctified in Christ Jesus, called to be saints, with all that in every place call upon the name of Jesus Christ our Lord, both theirs and ours:
2Ti 3:16 All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness:
If all Scripture is given by inspiration of God then Paul was just a messenger delivering a message to all that call upon the name of Jesus Christ. Wouldn't that include all believers in all places at all times?
Freind request accepted and may God bless your studies!