# a chosen people

"a people whom God has chosen" 

# a royal priesthood

Possible meanings are 1) "a group of priests who are also kings" or 2) "a group of priests who serve the king".

# a people for God's possession

"a people who belong to God"

# who called you out

"who called you to come out"

# from darkness into his marvelous light

"from a life of sin and ignorance of God to a life of knowing and pleasing him".