John Wesley on Revelation 15:6

And the seven angels came out of the temple - As having received their instructions from the oracle of God himself. St. John saw them in heaven, verse 1, Rev 15:1 before they went into the temple. They appeared in habits like those the high priest wore when he went into the most holy place to consult the oracle. In this was the visible testimony of God's presence. Clothed in pure white linen - Linen is the habit of service and attendance. Pure - unspotted, unsullied. White - Or bright and shining, which implies much more than bare innocence. And having their breasts girt with golden girdles - In token of their high dignity and glorious rest.