You can clarify that God is the one who has chosen them. AT: "a people whom God has chosen" (See: [[rc://en/ta/man/translate/figs-activepassive]])
# a royal priesthood
Possible meanings are 1) "a group of kings and a group of priests" 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
Here "darkness" refers to their condition as sinful people who did not know God, and "light" refers to their condition as people who do know God and practice righteousness. AT: "from a life of sin and ignorance of God to a life of knowing and pleasing him" (See: [[rc://en/ta/man/translate/figs-metaphor]])