Revelation 3:1 And unto the angel of the church in Sardis write; These things saith he that hath the seven Spirits of God, and the seven stars; I know thy works, that thou hast a name that thou livest, and art dead.
He that have thee Seven Spirits and the Seven Stars is addressing this church. Why is Jesus introducing himself as the one who have the Seven Spirits and the Seven Stars? The number "Seven is symbolical for completion or perfection. So the message that Jesus wants to convey to this church is that they are spiritually dead but need to be Spiritually perfected
This message is to the pastors of Sardis, they have the reputation of Christians, and consequently of being alive to God, through the quickening influence of the Divine Spirit; but they are dead they have not the life of God in their souls, they have not walked consistently and steadily before God, and his Spirit has been grieved with them, and he has withdrawn much of his light and power.
The Seven Spirits and the Seven Stars, what does scripture tells us about these:
Revelation 5:6 And I beheld, and, lo, in the midst of the throne and of the four beasts, and in the midst of the elders, stood a Lamb as it had been slain, having seven horns and seven eyes, which are the seven Spirits of God sent forth into all the earth.
Zechariah 4:10 For who hath despised the day of small things? for they shall rejoice, and shall see the plummet in the hand of Zerubbabel with those seven; they are the eyes of the LORD, which run to and fro through the whole earth.
2Chronicles 16:9 For the eyes of the LORD run to and fro throughout the whole earth, to shew himself strong in the behalf of them whose heart is perfect toward him. Herein thou hast done foolishly: therefore from henceforth thou shalt have wars.
Job 34:21 For his eyes are upon the ways of man, and he seeth all his goings.
Proverbs 15:3 The eyes of the LORD are in every place, beholding the evil and the good.
Jeremiah 32:19 Great in counsel, and mighty in work: for thine eyes are open upon all the ways of the sons of men: to give every one according to his ways, and according to the fruit of his doings:
Revelation 3:2 Be watchful, and strengthen the things which remain, that are ready to die: for I have not found thy works perfect before God.
Revelation 3:3 Remember therefore how thou hast received and heard, and hold fast, and repent. If therefore thou shalt not watch, I will come on thee as a thief, and thou shalt not know what hour I will come upon thee.
Revelation 3:4 Thou hast a few names even in Sardis which have not defiled their garments; and they shall walk with me in white: for they are worthy.
Revelation 3:5 He that overcometh, the same shall be clothed in white raiment; and I will not blot out his name out of the book of life, but I will confess his name before my Father, and before his angels.
Revelation 3:6 He that hath an ear, let him hear what the Spirit saith unto the churches.
(KJV)