a letter from the lord

In the first century, the best way to communicate out of town was with written correspondence.  There was no mail service.  The sender had to find someone heading that way and send the message or letter with them.  The epistles or letters of Paul were no exception.  Paul told the Corinthians: “You show that you are Christ’s letter, delivered by us, not written with ink but with the Spirit of the living God—not on tablets of stone but on tablets of human hearts.” (2 Corinthians 3:3 CSB17)
What was true for the Corinthians is also true for us! So we become the correspondence from God to the world.  We are a letter from the Lord to those who need to know. Praise God!