A question I’ve had recently is, “Were Paul’s letters written to me or others?” I’ve wondered, “Am I reading someone else’s mail or are Paul’s writings general information relevant to all believers?”
Let’s start with who Paul himself said his letters were written to:
1 Corinthians 1:2
2 Corinthians 1:1
Colossians 1:2 & 4:16
2 Thessalonians 1:1
1 Timothy 1:2
2 Timothy 1:2
So there you have it. It is notable that the only book which clearly states it was designed for the general audience of all Christendom is 1 Corinthians.
Two observations: 1) Paul told the Colossians to let the Laodiceans read their letter too. This could imply Paul felt his letter to the Colossians had broad application. 2) At the end of 1 Thessalonians Paul exhorts his letter be read to “all the brothers.” Again, this could mean he thought his letter had broad application to all of Christendom, or it may have just meant he wanted everyone in Thessalonica to hear it. In context, the latter seems to probable.
In conclusion, the answer to the original question of, “Who did Paul write his letters to?” is, “In general, not explicitly to us.” However, that doesn’t mean they are not applicable for us, or that they do not contain truth relevant for us today. I think they do. I’m just saying those conclusions require inference.