Revelation 1:4  . . . Grace to you and peace, from God . . . and from the seven Spirits who are before his throne

Revelation 3:1 He who has the seven Spirits of God . . . says . . .

Revelation 4:5  . . . There were seven lamps of fire burning before his throne, which are the seven Spirits of God.

Revelation 5:6  . . . a Lamb standing, 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.

Many Bible scholars see these as references to the Holy Spirit. Elsewhere in Revelation, angels are called angels and appear in angelic form, whereas the seven Spirits appear only as symbols (lamps or eyes).

The expression “grace and peace,” (Revelation 1:4) is a common way of commencing New Testament epistles but always as coming from a divine source (God and Christ). Check it out. It would be inappropriate to see created beings as a source of grace and peace.

Speaking of Jesus as having the seven Spirits (Revelation 3:1) and of the seven Spirits belonging to God and Jesus (Revelation 4:5; 5:6) is consistent with New Testament usage, such as:

Romans 8:9 But you are not in the flesh but in the Spirit, if it is so that the Spirit of God dwells in you. But if any man doesn’t have the Spirit of Christ, he is not his. (Emphasis mine.)

References to the seven Spirits in Revelation are reminiscent of:

Zechariah 4:6,10  . . . Not by might, nor by power, but by my Spirit . . . these seven  . . . are the Lord’s eyes, which run back and forth through the whole earth.

The seven in Zechariah are more than mere eyes because this same verse says, “. . . these seven shall rejoice . . .”

And consider these Scriptures:

Zechariah 6:5 These are the four spirits of heaven, going out from standing in the presence of the Lord of the whole world. (NIV – emphasis mine).

Isaiah 11:2 The Lord’s Spirit will rest on him:
the spirit of wisdom and understanding,
the spirit of counsel and might,
the spirit of knowledge and of the fear of the Lord.

With a stretch, you could turn this last verse into seven aspects of the Spirit, but the more natural division is three (or six if you separate wisdom and understanding, and so on).

So even when going beyond the mystery of three persons in one, down to just one member of the trinity, there still seems to be some sort of plurality. Moreover, there being mention of seven, four and three suggests the Holy Spirit is plural, not just in one sense, but in several.