‘Now therefore, if you will indeed obey my voice and keep my covenant, you shall be my treasured possession among all peoples, for all the earth is mine;  and you shall be to me a kingdom of priests and a holy nation.’ These are the words that you shall speak to the people of Israel.Exodus 19:5-6 (ESV)
These were the words God called upon Moses to deliver to His people. They had seen how He delivered them from Egypt. They’d seen His saving power. Now, they would hear His voice in what is one of the most famous sections in all of Scripture: the Ten Commandments. The Lord is a God who acts decisively and speaks clearly for His people–who are to be a kingdom of priests and a holy nation. God’s people were to be a people who showed the world what God is like.
Fast forward to 1 Peter 2:9, and the same voice is heard again, “But you are a chosen race, a royal priesthood, a holy nation, a people for his own possession, that you may proclaim the excellencies of him who called you out of darkness into his marvelous light” (ESV). This time, it isn’t just the people of Israel but everyone who believes in Jesus who hears these words. He called Israel out of Egypt. He called us out of darkness, that His light would shine through us. The church is to be a people who show the world what God is like.