^5:8 And when He had taken the book, the four living creatures and the twenty-four elders fell down before the Lamb, having each one a harp, and golden bowls full of incense, which are the prayers of the saints.

And when HE had taken the BOOK, the four living creatures and the twenty-four ELDERS

The first hymn is sung by these 28 .... later hymns are sung by all creation.

FELL DOWN before the LAMB, having each one

This shows equivalence between the LAMB and diety. The 24 elders representing redeemed saints along with the 4 mightest heavenly creatures/angels give due homage.

The inheritance is about to be fulfilled. This implies the 28 must have some idea of the awesome contents of the book and seals.

a HARP and

God loves beautiful music. It was part of temple worship, Ezra 3:10-11. The harps are part of the music before the Lamb on Mount Zion, Revelation 14:2. The victorious ones in Revelation 15:2 are holding harps of God.

golden bowls (vials) full of incense, which are the prayers of the saints.

We see these prayers of the saints again at the breaking of the seventh seal and at the preparation for the blowing of the seven trumpets, Revelation 8:3-4. These prayers may also be the "avengence prayers" of the martyrs, Revelation 6:10.