Christ died for our sins once and for all ... what a great promise/revelation. That no longer are we bound by the laws of sin, with no choice of doing what is right, but we are now free from the bonds of sin that easily entangles us. Peter also uses the flood in Noah's time as an illustration of baptism, how the old and corrupt of that world was washed away, so that Noah and his family could begin anew. Christ has saved us from the old ways. We now can have a new life, a new beginning because of what He has done on the cross for us.
This passage also mentions that Christ preached to the spirits in prison whom had rejected the ways of God back in Noah's time. Jesus was proclaiming his victory over death, that sin no longer has hold over us. I'm also wondering if he preached redemption to those spirits in prison (3:18-19). What did he preach? Peter doesn't tell us in this letter, but his emphasis was on the symbol of baptism, and letting us know that Christ is at God's right hand "with angels, authorities and powers in submission to him."
Peter tells us that Christ is sitting at God's right hand with authority and power. What a great hope we have in Christ, but it is real hope, not a hope that is wishful thinking, but a hope that is built on the promises of God, and the knowledge of what God has already done for us.