If we accept that the person speaking to John in Rev 1 is Jesus, that is the one who is:
- Walking among the lampstands (v13)
- the Son of Man (v13)
- long robe and golden sash around His chest (v13)
- hair like wool, white as snow (v14)
- eyes like blazing fire (v14)
- feet like polish bronze (v15)
- Voice like many waters (v15)
- held 7 stars in right hand (v16)
- sharp double-edged sword from mouth (v16)
- face like the sun (v16)
- First and Last (v17)
- was dead but now alive forever (v18)
- Holds the keys to death and hades (v18)
Then it is a simple matter to determine who is speaking to each of the seven churches.
Ephesus
- He who hold 7 stars in right hand
- walks among the 7 lampstands
... ie, Jesus according to Rev 1.
Smyrna
- first and last
- dead but now lives again
... ie, Jesus according to Rev 1.
Pergamum
- he who has the sharp two-edged sword from the mouth
... ie, Jesus according to Rev 1.
Thyatira
- Son of God
- eyes like blazing fire
- feet like burnish bronze
... ie, Jesus according to Rev 1.
Sardis
- holds 7 spirits of God
- Hold 7 stars in hand
... ie, Jesus according to Rev 1.
Philadelphia
- holy and true
- holds Keys of David to door shuts and no one can open etc.
... ie, Jesus according to NT theology
Laodicea
- Amen
- faithful and true
- ruler of God's creation
... ie, Jesus by NT theology.
Note that most of the titles for Jesus in the seven churches are taken from the description in Rev 1. It is also there that Jesus instructs John to write what Jesus is about to tell him, Rev 1:11.
Thus, Jesus is the one speaking throughout Rev 1, 2, 3.
This is all very well but what do we do with the seven times that we read, "let him hear what the Spirit says to the seven churches", Rev 2:7, 11, 17, 29, 3:8, 12, 22? This is actually less complicated than it appears.
The seven messages in Rev 2 & 3 are spoken by Jesus to John (via an angel, Rev 1:1-3). HOWEVER - having conveyed these messages to the churches, each member of every church 9then and since) must accept and understand those message which is only possible by the enlightenment of the Holy Spirit. Note this well-known verse:
1 Cor 2:14 - The person without the Spirit does not accept the things
that come from the Spirit of God but considers them foolishness, and
cannot understand them because they are discerned only through the
Spirit.
See also John 16:13, etc. Therefore, while Jesus speaks the messages to john (who records them for us) we must understand and "hear" them by means of the Holy Spirit. Therefore, Jesus asks that each person listen or "hear" what the Spirit is saying in these messages to the seven churches.