What does 1 Peter 1:16 mean?

Verse 16 finishes the thought begun in verse 15. Peter quotes a well-known command of God to His people Israel (Leviticus 11:44–45; 19:2; 20:7). He does this to drive home a point, particularly to his Jewish readers, that God has always commanded His children to "be holy." It's not a new idea.

Verse 15 and 16 can seem daunting, at first. The command to be as holy as God seems like an impossible task. But God isn't giving us a hopeless requirement. It's helpful to look at the passages Peter is quoting from to better understand what the word "holy" means to God. For Israel, it was very much about living differently from the other nations around them. To be "holy"—literally, "set apart"—meant to refuse to eat certain foods or wear certain clothes. To be holy meant respecting your parents. To be holy meant to keep God's commands. God's desire for His people was to be like Him, and He is holy. That's still His desire. The difference between the holiness commanded in the Old Testament and what's here is found in what Peter has already written in this letter. That is, God has already made us holy in Christ. He has already set us apart and saved us. Now he calls us to make choices that reflect who we already are.

In other words, Christians are called to change our conduct to fit our identity. As holy people, we shouldn't be "okay" with our sin. We shouldn't accept falling into the old patterns. We are to act as holy people act. Will we make perfectly sinless choices in this life from here forward? No. We still rely on God's grace and forgiveness. Is God's standard for us now that we would live in perfect holiness? Yes, and it should become our standard for ourselves, as well, even if we won't achieve it until we are with our Father in eternity.