Symbolism
The spirits of God are symbolically represented by a seven-headed candlestick that stood before His presence in the wilderness tabernacle (later the temple in Jerusalem, see Numbers 8:1 - 2). Most of the references, however, to the seven spirits of (or from) God are found in the book of Revelation.
. . . Grace and peace be to you from Him Who is, and Who was, and Who is to come; and from the seven spirits that are before His throne (Revelation 1:4, HBFV throughout).
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 . . . (Revelation 3:1).
And proceeding from the throne were lightnings and thunders and voices; and seven lamps of fire, which are the seven spirits of God, were burning before the throne (Revelation 4:5, see also 5:6).
Spiritual Perfection
The number seven is referenced more times in Scripture than any other number. It is usually used to designate wholeness or perfection in general (either of a physical or spiritual nature). As such, it does not necessarily mean an exact number of something (e.g., Jesus obviously has more than this low number of divine traits, characteristics, or gifts).
What is Referenced?
In Isaiah 11, the prophet is clearly offering a prophecy concerning Jesus Christ. Although the prophecy can refer to his first coming as Savior to die for man's sins, it primarily references Jesus' second coming when he sets up the Kingdom on earth as King of King and Lord of Lords.
The first verse of Isaiah 11 states, "And there shall come forth a shoot out from the stump of Jesse, and a BRANCH shall grow out of his roots" (Isaiah 11:1).
Six of the seven gifts that will rest or abide in Christ are obvious in verse 2. They are given in three sets of two each. They are wisdom and understanding (both related to the intellect and discernment), counsel and might (both practical in nature), plus knowledge and the fear of the Eternal (which relates to the relationship with the Father).
The last of the seven, also recorded in Isaiah 11:2, is easily overlooked. It is the spirit of the Lord (Jehovah), which is found at the beginning of the verse and which makes everything possible.
Evidence that Isaiah is primarily prophesizing concerning Jesus Christ's second coming (and afterwards) is found after verse 4 of chapter 11. These verses discuss the fact that the Lord, when he returns to rule the earth, will righteously judge in favor of the poor and meek.
Jesus will rule all mankind from Jerusalem for 1,000 years (known as the Millennium). Admittedly, the twisted logic of those who promote the false doctrine of the Trinity can make understanding the seven (7) spirits of God more difficult than it needs to be.