Rev 5:6

6 I saw in the midst of the throne and of the four living creatures, and in the midst of the elders, a Lamb standing, as though it had been slain, having seven horns, and seven eyes, which are the seven Spirits of God, sent forth into all the earth. 

seven horns and seven eyes which are the seven Spirits out God sent out into all the earth – the seven eyes are the seven spirits of God described in Zech 4:10. A horn generally symbolizes power; see 1 Sam 2:1, Rev 13:1, etc. Seven means perfection, or completeness. The meaning here is the same as Rev 1:16; and Rev 1:20: the Spirit of Christ as the Ruler of the Angels, and the Son of Man, holds seven Angels in His right hand. Dan 8:11 and Rev 12:9 tell us that the Spirit of Christ became the “Captain of the captains” when He became our Lord [Prince and Captain are the same Hebrew word].  Therefore, the seven horns also represent complete authority over the Angels.