Seven is a common number found often throughout the Scripture. There are seven years of famine Gen 41:46-57 the 7 years of plenty (Gen. 42:28). Joshua marched 7 days, had 7 priests blowing 7 trumpets round the walls of Jericho, and marched seven times on the 7th day (Neh. 9:6). The leprous Naaman was ordered to bathe 7 times in the Jordan (2 Kings 6:15). There are seven beatitudes, seven petitions in the Lord's Prayer; 7 parables of the Kingdom in Mt 13:1-58; 7 woes pronounced on the Pharisees (Mt. 23:13,15-16,23,25,27,29), seven loaves, seven phrases from the cross, etc.

In the book of Revelation the number 7 is prominent. (The book is structured by the use of numbers seven, four, and three). Throughout Johns Apocalypse (unveiling of Jesus Christ) the number seven is most often used. There are sevenfold divisions of the church seven judgments Rev 1:4. There are 7 seals (Rev 7:2); a lamb with 7 horns and 7 eyes (Rev. 7:7); 7 angels with 7 trumpets (Rev. 8:2); 7 thunders (Rev 10:3); a dragon with 7 heads and 7 diadems (Rev 13:3); a beast with 7 heads (Rev19:9); 7 angels having the 7 last plagues (Rev 15:1); and 7 golden bowls of the wrath of God (Rev 15:7) and a scarlet-colored beast with 7 heads (Rev 18:17) which are 7 mountains (Rev 18:23) and 7 kings (Rev. 18:24).

The number seven throughout the Scripture expresses totality or completeness.

Rev. 1:4 John, “to the seven churches which are in Asia: Grace to you and peace from Him who is and who was and who is to come, and from the seven Spirits who are before His throne.”

This Scripture should not be interpreted as 7 Holy Spirits who are God himself. Jesus refers to the Holy Spirit called the comforter for the believer.

Rev. 1:4: “To the seven churches which are in Asia.” “Rev 1:4 Revelation does not include Colossae, Miletus, Hierapolis, or Magnesia. The seven named are chosen to symbolize the whole Church. Compare Rev 2:7. Seven being the number of the covenant, we have in these seven a representation of the Church universal.” (from Vincent's Word Studies of the New Testament)

All believers learn and are able to see themselves in these 7 churches that represent the whole.

there are seven ministering angels before this throne referred to in Jonathan ben Uzziel's Targum on Gen 11:7: God said to the SEVEN ANGELS which stand before him, Come now,…

The same concept is used in Isaiah 11:2 describing the branch (Jesus) that will have “The Spirit of the LORD shall rest upon Him, the Spirit of wisdom and understanding, the Spirit of counsel and might, the Spirit of knowledge and of the fear of the LORD.” This describes the various attributes of the Holy Spirit, His sevenfold aspects of perfection and totality that accompanied Jesus as He ministered on earth.

This term seven Spirits is found exclusively in the Book of Revelation of Jesus Christ and is used 4 times by John.

Rev 3:1:  “And to the angel of the church in Sardis write, 'These things says He who has the seven Spirits of God and the seven stars:" Notice it says who has (not is) the seven spirits of God.

Seven here is the fullness of the Spirit, the seven stars is the light of the seven churches. As stated, the epistle is to the church at Sardis (Rev 1:16 He had in His right hand seven stars.) Corresponding to "the seven churches.”

Rev. 4:5: “And from the throne proceeded lightnings, thunderings, and voices. Seven lamps of fire were burning before the throne, which are the seven Spirits of God.

There are seven lamps of fire burning before the throne, which are the seven Spirits of God. This again refers to Isa. 11 and the seven attributes of the (one) Holy Spirit.

Much like the 7 branched lampstand in the tabernacle/temple that gave light in the holy place. The lamps are emblematic of the seven Spirits of God. Lamps were filled with oil to give light in biblical times. They represent the various influences of that Spirit in the church in the world or the operations of that Spirit

Rev. 5:6: “And I looked, and behold, in the midst of the throne and of the four living creatures, and in the midst of the elders, stood a Lamb as though it had been slain, having seven horns and seven eyes, which are the seven Spirits of God sent out into all the earth.”

The lamb is described symbolically having seven horns and seven eyes which is also said to be the seven spirits. The seven eyes are resting on the stone laid by Yahweh (Zech. 3:9 shows the branch, who is a man is the stone the builders rejected).

The most sound and relative interpretation for this phrase seven Spirits of God is that it emphasizes the totality of the Spirit: “There is the one Holy Spirit with seven manifestations here to the seven churches (Swete, The Holy Spirit in the New Testament, p. 374), unity in diversity (1 Cor 12:4)” (from Robertson's Word Pictures in the New Testament).