^3:13 `He who has an ear, let him hear what the Spirit says to the churches.'

He who has an ear, let him hear what the Spirit says to the churches.

The route of the letters to the churches is amazing. While it appears that the route is through many agents, it really was directly from the Holy Spirit/Lord all the time.

Holy Spirit
| Lord (Revelation 1:1)
| |
| |—> angel (Revelation 1:1)
| |
| |—> John (Revelation 1:1)
| |
| |—> Church's angel (Revelation 3:7)
| |
|—--------------------|-> Church at Philadelphia

Who at the Church at Philadelphia received this letter?

Given what we have studied about the Philadelphian Church, the most likely person was the "overcomer" (Revelation 19:7). That person has their citizenship paper (previous verse).