Paul is writing to the Corinthians. The first two sentences are a typical greeting and introduction to the letter. It appears to be a pleasant greeting, just a letter between old friends. Paul then continues thanking God for the people of Corinth. Reminding them of what they have learned, or as Paul says it, what they have received from Paul. And Paul reminds them that God is always faithful.
Why would he have to remind the people of Corinth that God is always faithful? It could be he no longer has anything positive to say. If you know the story of Corinth saying that God is always faithful is like a warning about what is to come.
Corinth is a coastal city in Greece on the Mediterranean. As with most seafaring cities their reputation is not the best. And at Corinth, because of so many cultures being blended from so many different locations just about any imaginable pagan god was well entrenched.
Paul braves the difficult situation to share the message of Jesus. As Paul indicated, the people received his message, but apparently, they were forgetting and were falling back into their old lifestyle. Paul is calling them to task. Saying God is always faithful implies that they are no longer faithful and need to make a change of heart. To remember what they have been taught. They need to return to God.
If somebody were watching you, would they recognize you as someone filled with faith?
May the Lord bless you in the name of the Father and of the Son and of the Holy Spirit. Amen