That is a matter of some conjecture. There are three New Testament scriptures that reference the "Seven Spirits" of God (Rev 3:1, 4:5,5:6). Below is the opinion of a two commentaries each on all three verses.
From Albert Barnes Notes on the Bible:
Which are the seven Spirits of God sent forth into all the earth - See the notes on Rev_1:4. That is, which represent the seven Spirits of God; or the manifold operations of the one Divine Spirit. As the eye is the symbol of intelligence - outward objects being made visible to us by that - so it may well represent an all-pervading spirit that surveys and sees all things. The eye, in this view, among the Egyptians was an emblem of the Deity. By the “seven Spirits” here the same thing is doubtless intended as in Rev_1:4; and if, as there supposed, the reference is to the Holy Spirit considered with respect to his manifold operations, the meaning here is, that the operations of that Spirit are to be regarded as connected with the work of the Redeemer. Thus, all the operations of the Spirit are connected with, and are a part of, the work of redemption. The expression “sent forth into all the earth,” refers to the fact that that Spirit prevades all things The Spirit of God is often represented as sent or poured out; and the meaning here is, that his operations are as if he was sent out to survey all things and to operate everywhere. Compare 1Co_12:6-11.
And:
These things saith he that hath the seven Spirits of God - See the notes on Rev_1:4. If the phrase, “the seven Spirits of God,” as there supposed, refers to the Holy Spirit, there is great propriety in saying of the Saviour, that he has that Spirit, inasmuch as the Holy Spirit is represented as sent forth by him into the world, Joh_15:26-27; Joh_16:7, Joh_16:13-14. It was one of the highest characteristics that could be given of the Saviour to say, that the Holy Spirit was his to send forth into the world, and that that great Agent, on whose gracious influences all were dependent for the possession of true religion, could be given or withheld by him at his pleasure.
And:
Which are the seven Spirits of God - Which represent, or are emblematic of, the seven Spirits of God. On the meaning of the phrase, “the seven Spirits of God,” see the notes on Rev_1:4. If these lamps are designed to be symbols of the Holy Spirit, according to the interpretation proposed in Rev_1:4, it may be perhaps in the following respects:
(1) They may represent the manifold influences of that Spirit in the world - as imparting light; giving consolation; creating the heart anew; sanctifying the soul, etc.
(2) they may denote that all the operations of that Spirit are of the nature of light, dissipating darkness, and vivifying and animating all things.
(3) perhaps their being placed here before the throne, in the midst of thunder and lightning, may be designed to represent the idea that - amidst all the scenes of magnificence and grandeur; all the storms, agitations, and tempests on the earth; all the political changes; all the convulsions of empire under the providence of God; and all the commotions in the soul of man, produced by the thunders of the law - the Spirit of God beams calmly and serenely, shedding a steady influence over all, like lamps burning in the very midst of lightnings, and thunderings, and voices. In all the scenes of majesty and commotion that occur on the earth, the Spirit of God is present, shedding a constant light, and undisturbed in his influence by all the agitations that are abroad.
From John Gill's Exposition of the Whole Bible:
and seven eyes, which are the seven spirits of God sent into all the earth; which some understand of angels, and of a sufficient number of them, which belong to Christ, and are at his command, and who are ready to do his will, and to be sent forth by him, into the several parts of the earth, to execute his pleasure: but these rather design the Spirit of God and his gifts, which Christ received without measure, both in his human nature, at his incarnation, and after his resurrection from the dead, and ascension; which he bestowed on his apostles and ministering servants, whom he sent forth into all the world, to preach his Gospel with them; and which he has, more or less, ever since continued to do. The Ethiopic version reads in the singular number, "and this is the Spirit of God which is sent into all the earth"; See Gill on Rev_1:4; these "seven eyes" may design the perfect knowledge of Christ, his foresight of future events, and his all wise providence, which is always and everywhere concerned to fulfil and accomplish them; so that he is every way qualified to take the book of future events, as to the church and world, and reveal it, open and explain it, and fulfil the things contained in it; see Zec_3:9.
And:
these things saith he that hath the seven spirits of God; the fulness and perfection of the gifts and graces of the Spirit of God, as in Rev_1:4, which Christ, as Mediator, has without measure, and are at his dispose, and which he, having received for men, gives unto them; and at the time of the Reformation bestowed them on many eminent servants of his in a very plenteous manner; for which reason he assumes this character in writing to this church:
And:
which are the seven spirits of God; in allusion to the seven lamps in the tabernacle and temple, which were trimmed by the priests, and always kept burning, and are expressive of the Spirit, and his gifts; and these being signified by the number "seven", denote the fulness and perfection of them; and being said to be "before the throne", show that there is always a sufficiency of them for the supply of the churches in all ages, to fit and qualify proper persons to minister the word, and administer ordinances; and these being called "lamps of burning fire", point at the light the Spirit of God in his gifts communicates to the churches; and that warmth and heat, comfort and refreshment; conveyed to them, through the preaching of the Gospel, and the dispensation of the ordinances of it, under his illuminating and quickening influences.