ANSWER: The seven 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, in the Bible that mention these 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)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 . . ." (3:1).
5. 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).
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 is being referenced (e.g., Jesus obviously has more than this low number of divine traits, characteristics, or gifts). It is many times used to convey the idea of completeness or fullness.
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. Verse one of the chapter 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 spirits (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 seventh, also in verse 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 the same chapter. This verse discusses that fact that the Lord will righteously judge in favor of the poor and meek on the earth, and will firmly rule the entire earth. These actions will not take place until Christ returns, conquers the forces of evil on earth, and then rules 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 spirits of God more difficult than it needs to be.