# Sardis

This is the name of a city in the western part of Asia that today is modern Turkey. See how you translated this in Revelation 1:11.

# the seven spirits

The number seven is a symbol of completeness and perfection. The "seven spirits" refers either to the Spirit of God or to seven spirits who serve God. 

# the seven stars

These stars are symbols that represent the seven angels of the seven churches. 

# You have a name that you are alive

"You have a reputation for being  alive" or "People think that you are alive" 

# alive ... dead

Obeying and honoring God is spoken of as being alive; disobeying and dishonoring him is spoken of as being dead.