There is just to much stuff here to try to title into one subject. This passage, 2 Peter 2:4-12, has always been one of my favorite passages to preach and teach from. Here's why.
Peter points out that Jesus is a living cornerstone and that we are living stones. One of my youth years ago asked me if that meant we were blockheads for Jesus? I said yes. Peter's point is obvious. We are a living temple and we are a people who make up a living temple that honors, worships, repents and is used to spread the Gospel all over the world.
In verse 6 it says "...the one who trusts in him will never be put to shame." Paul says in Rom 1:16 that he is not ashamed of the Gospel of Jesus. Peter tells us that the Gospel will make us be ashamed of Jesus. Literally, the phrase means that we will never be frustrated, confused, be in fear of, hopeless or ashamed of being a Christian.
In verse 9 Peter says that we are a chosen people. Chosen is like when in school you would raise your hand and the teacher choose you. When we "raise our hand" and ask Jesus to forgive us of our sins He promises to choose us!. A royal priesthood is weird. Priests decended from priests and royalty decends from royalty. So how do you get a royal priesthood? We are sons and daughters of the King of king, our Father in Heaven. Therefore, if He is the King, we are royalty who can also interceed (priesthood) in His presence. A people belonging to God. We know that He has redeemed (bought us back) from sin. But the phrase here means that we are the possession of God. You have seen the t-shirts "Property of . . . " Well we are the property of God.
Now we can declare the good works of God, the one who pulled us out of the dark. Not because we are that good, but because of His mercy that changed us. Live a good life (one that honors God) in front of "spiritual" people. (New Agers and the like) Peter here calls them pagans and pagans were people who worshipped false gods in greek temples. Then they will praise God the day that He comes to oversee, visit and bless them.