We have met with the sea of glass before in chapter 4 of the Book of Revelation. John looks into heaven itself where, before the throne of God, there is a great sea of crystal.
We are allowed music in worship and simple instruments. In the Old Testament, only harps and lyres were allowed in the synagogues, in the places of assembly for worship to accompany the psalms. In the temple there were two more instruments permitted. But no more than four. There was a great restriction on the instrumentation. There could be many instrumentalists because the temple contained a vast crowd and there were all the people in the outer courts and outside, but it was kept simple.