Revelation is a puzzling mystery, and this is just one of those questions we may never unlock.
Here's a post from gotquestions.org that addresses this question. They aren't sure what to make of it either, but they do give the verse you cited as a possibility:
Question: "What are the seven spirits of God?"
Answer: The "seven spirits of God" are mentioned in Revelation 1:4;
3:1; 4:5; and 5:6. The seven spirits of God are not specifically
identified, so it’s impossible to be dogmatic. Revelation 1:4 mentions
that the seven spirits are before God's throne. Revelation 3:1
indicates that Jesus Christ "holds" the seven spirits of God.
Revelation 4:5 links the seven spirits of God with seven burning lamps
that are before God's throne. Revelation 5:6 identifies the seven
spirits with the "seven eyes" of the Lamb and states that they are
"sent out into all the earth."
There are at least three possible interpretations of the seven spirits
of God. The first is that the seven spirits of God are symbolic of the
Holy Spirit. The Bible, and especially the book of Revelation, uses
the number 7 to refer to perfection and completion. If that is the
meaning of the “seven” in the "seven spirits," then it is not
referring to seven different spirits of God, but rather the perfect
and complete Holy Spirit. The second view is that the seven spirits of
God refer to seven angelic beings, possibly the seraphim or the
cherubim. This would fit with the numerous others angelic beings that
are described in the book of Revelation (Revelation 4:6-9; 5:6-14;
A third possibility is based on Isaiah 11:2, which says, “The Spirit
of the LORD will rest on him — the Spirit of wisdom and of
understanding, the Spirit of counsel and of power, the Spirit of
knowledge and of the fear of the LORD.” This could possibly explain
the seven spirits of God: (1) Spirit of the LORD, (2) Spirit of
wisdom, (3) Spirit of understanding, (4) Spirit of counsel, (5) Spirit
of power, (6) Spirit of knowledge, (7) Spirit of the fear of the Lord.
The Bible doesn’t tell us specifically who/what the seven spirits are,
but the first interpretation, that they are the Holy Spirit, seems the
Personally, I lean towards these spirits being angelic members of the Divine Council, but that is by no means clear.
5Let the heavens praise your wonders, O LORD, your faithfulness in the
assembly of the holy ones! 6For who in the skies can be compared to
the LORD? Who among the heavenly beings is like the LORD, 7 God
greatly to be feared in the council of the holy ones, and awesome
above all who are around him?