"the angel whom St John saw in the sun"
The angel of revelation by William Blake
Public DomainThe angel of revelation by William Blake

This a reference to the Book of Revelation, the last book in the Bible. One of the most extreme and unsettling biblical texts, it describes the vision St John the Divine had of the end of the world and the judgment that was to follow.

The angel St John saw is described as holding seven stars and having a face that shines like the sun.