1 Peter 2:10

10 for you once were NOT A PEOPLE, but now you are THE PEOPLE OF GOD; you had NOT RECEIVED MERCY, but now you have RECEIVED MERCY.

Speaking to both believing Jews and Gentiles, Peter reminds them that they were “called out of darkness.” And in that state they were not the people of God but were of the devil and of darkness. In fact, Peter writes that they were “not a people.” I suppose he meant that being always guided by their fleshly desires, they were more like animals than people. Hence, they also did not receive God’s mercy. But when they came to the light and believed they were privileged as Children of God to receive His mercy.