Peter is continuing his discourse on what Christ did and who Christ is, telling us in v. 20 that "He was foreknown before the foundation of the world..." Jesus is God who has lived eternally past and will live eternally in the future. But why did he come? Peter answers that immediately - he came for our sake, the sake of those who are believers in God through Jesus. Christ came into human history for my sake and for your sake. He didn't just come to give us truth, to be the truth, which he was and still is today. He came for us, so that we could belong to our Heavenly Father. God the Father raised Christ from the dead and gave him glory so that our faith and hope are in God, Peter goes on to explain. The "so that" is important here as it shows the purpose for which God raised Jesus from the dead. In some way it seems to me that the resurrection, while of course necessary in the salvation plan of God, also served to increase our faith and hope in God himself. We believe God and hope in him because Christ was risen from death. He conquered it, and God will conquer it for us as well. My hope does not have to be rooted in what I can do anymore, nor do I have some vain "hope" that in the end I've done enough for God to accept me. He has accepted me and given me a new and living hope, as Peter has already mentioned, through the resurrection of Jesus.
Peter begins a new thought in v. 22, moving from the explanation of who Jesus is and what God has accomplished into exhorting believers toward maturity in Christ. His basic message is this: because of all God has done, love one another from a pure heart. The super-natural response for each individual Christian is to NOT keep it to themselves but to share this love that God has given them with others. Specifically Peter has in mind Christians loving other Christians - this does not mean we are only to love Christians and shun non-Christians, but rather the point here is that there needs to be a mutual love for one another because of what God has done in each heart. The line of reasoning for v. 22 and 23 could go something like this: Since you have been born again to a new life following Jesus, obey Christ's greatest commands to love God and love one another in brotherly (and sisterly) love. The important idea is "since" - that is, because God has given you new life, a new and living hope in Jesus, the response must be one of love. And as the world sees our love for one another - which must be different and deeper than the world's vain version of love - spiritual light is reflected in our Christian communities to a world desperately in need of light.
The idea of being "born again" (in v. 23) is one of the best known and most mocked ideas in all of Christianity. Yet it comes up several times in Peter's writing, and he obviously gets it from Christ. Here's the deal: you simply can't get away from the fact that conversion is like a new birth. You were born into futility in this world, spiritually dead, blind, and dumb. You cannot save yourself and the only hope you have is for God to do a supernatural work and re-birth you and me. While there are many ways to describe what happens to someone when they become a Christian, one inevitable fact remains: they are born-again as Christians. What I find ridiculous is when people say "born-again Christian" as if there is another kind of Christian. There isn't. If you're a Christian, you're a born-again Christian. I will be the first to admit that I get uncomfortable at the questions some pose, such as "So are you a 'born-again' Christian?" But the fact remains that this is exactly what happened. I once was dead and now am alive. I once had no true hope and now have a living hope because I belong to a living Savior and the only true living God, my Heavenly Father. Born again is exactly what happened, and if you're not born again you're not a Christian. This new birth is of "imperishable seed" Peter goes on to explain. This is because my first birth was natural (though the birth process is amazing, it is still natural) and this second birth is super-natural. It is the coming to a knowledge of Jesus Christ that so changes you that you're literally re-born.
Peter then uses the Old Testament to say something that the Bible says over and over in different ways: you and I are a blip on the radar of human history, like the grass in a field or a flower in a garden. If this were a movie, you would be in it for, oh I don't know, 0.3 seconds or less. You'd have to try and pause the scene at just the right time so your friends could see you in the far back-drop of the scene. We are not the main Characters... God is. We are not the main point... He is, and His Word stands forever. It cannot be stamped out, killed out, chased out, legislated out, or anything else. Verse 25 says "And this word is the good news that was preached to you." This good news about Jesus that Peter was inspired to proclaim will stand forever, changing the lives of all who receive it in faith. Praise his name.