A royal priesthood

“But you are a chosen people, a royal priesthood, a holy nation, a people belonging to God, that you may declare the praises of Him who called you out of darkness into His wonderful light.” 1 Peter 2:9
Here are four descriptors of believers: a chosen people, a royal priesthood, a holy nation, a people belonging to God. These are all used of Israel: they were chosen by God (Deut. 10:15), they were a holy nation and kingdom of priests (Ex. 19:6), a people belonging to God (Lev. 25:55).
The term ‘royal priesthood’ is interesting to note. In the epistle to the Hebrews, the writer spends a whole chapter (ch. 7) describing the priesthood of Melchizedek and how it is different to the Aaronic priesthood. Under Judaism, it was impossible for a king to be a priest, or for a priest to be a king. Priests were descended from the tribe of Levi (and specifically from Aaron), while kings were descended from the tribe of Judah (specifically, David). But in Gen. 14:18 we are introduced to this mystery man Melchizedek, who was the king of Salem and a priest of God. It is this priesthood that Jesus belongs to – an eternal one, not based on the Levitical law (Heb. 7:24). And it is this priesthood that if we are in Him, we belong to too. Like Israel, we have been chosen by God (John 15:16, 2 Thess. 2:13), we are made holy (Col. 3:12, etc.), and we belong to Him (Rom. 14:8, etc.).