John,
To the seven churches in the province of Asia:
Grace and peace to you from him who is, and who was, and who is to come, and from the seven spirits before his throne,
Revelation 1:4
John was in exile writing from a small island called Patmos about 36 miles off the western coast of the province of Asia Minor. He received a revelation of Jesus and from Jesus while there. He wrote it down and sent it to seven major churches of Asia Minor: Ephesus, Smyrna, Pergamum, Thyatira, Sardis, Philadelphia and Laodicea.
These seven cities were each located about 50 miles apart in a clockwise circuit starting in Ephesus. John’s letter would have likely been delivered from church to church in this circuit. If you can imagine an oval shaped clock where 9 and 3 are closer than 12 and 6. The circuit would have been as follows starting with Ephesus on the western coast of Asia Minor: Ephesus (at 9 o’clock), Smyrna (at 10 o’clock), Pergamum (at 11 o’clock), Thyatira (at 12 o’clock), Sardis (at 1 o’clock), Philadelphia (at 2 o’clock) and Laodicea (at 3 o’clock).
The number seven is a significant biblical number. Seven is a number of perfection and completion. Jesus intended that this revelation be sent not only to the seven churches of Asia Minor but also to the Church as a whole.
This is also the first of several reverences to the seven spirits or the seven Spirits of God (sometimes translated as the sevenfold Spirit).
“To the angel of the church in Sardis write: These are the words of him who holds the seven spirits of God…
Revelation 3:1
From the throne came flashes of lightning, rumblings and peals of thunder. In front of the throne, seven lamps were blazing. These are the seven spirits of God.
Revelation 4:5
This doesn’t mean that the Holy Spirit is seven spirits. This is more of a reference to the Holy Spirit’s presence in each of the seven churches. Each believer has the Holy Spirit in them but that doesn’t mean there are 2 billion Holy Spirits. Again, the number seven points to the perfection or holiness of the Spirit of God. It’s also an allusion to the sevenfold characteristics of the Spirit of God mentioned in Isaiah 11:
A shoot will come up from the stump of Jesse;
Isaiah 11:1-2
from his roots a Branch will bear fruit.
The (1)Spirit of the Lord will rest on him—
the (2)Spirit of wisdom and of (3)understanding,
the (4)Spirit of counsel and of (5)might,
the (6)Spirit of the knowledge and (7)fear of the Lord—
The Spirit of God, the Spirit of Christ, the Spirit of Jesus, the Spirit of your Father, the Spirit of the Lord, the Spirit of holiness, the Spirit of Truth, the sevenfold Spirit, the seven Spirits of God are all different references in the New Testament to the one and only Holy Spirit. They are just different names–different ways of describing who the Spirit is and what characteristics He has.