1 Peter 3: 18 - 22
18 For Christ also died for sins once and for all, the just for the unjust, so that He might bring us to God, having been put to death in the flesh, but made alive in the spirit;
19 in which also He went and made a proclamation to the spirits now in prison,
20 who once were disobedient, when the patience of God kept waiting in the days of Noah, during the ark's construction, in which a few, that is, eight persons, were brought safely through the water.
21 Corresponding to that, baptism now saves you — not the removal of dirt from the flesh, but an appeal to God for a good conscience — through the resurrection of Jesus Christ,
22 who is at the right hand of God, having gone into heaven after angels, authorities, and powers had been subjected to Him.
A secure anchor is often the key to surviving a fierce storm or to simply remaining attached and protected when buffeted by wind or strong currents. Sailors or fishermen have found that their safety and success often depend on an anchor, at least in part. Life needs anchors. So many things are uncertain, and the greatest uncertainty (apart from the Word of God) is the question of what follows death. Many people refuse to think about death. They stoically stare straight ahead with no reaction or engagement on the matter, as if ignoring it eliminates it (I see way too much of that while ministering at funerals). There are also many perplexities as you live from day to day. Finances, health, relationships, job, equipment maintenance, school, neighbors — all these areas and many more can bring stress, doubt, or fear into your life. So let's talk about Peter's anchors, which will keep you centered, balanced, focused, and victorious.
The first anchor is Jesus and all that He has done for you. He once and for all died for your sins! The just for the unjust. Why? So that He could bring you to God. The only way to pay for sin is with death and shed blood. OK, Jesus died and shed His blood for you. Your death issues are eternally resolved when you believe in Him as your Savior and Lord. Further, He may have died in the flesh (natural), but He was made alive in the spirit (supernatural). It's that aspect of Jesus' resurrection that is so awesome. By transforming His human body into a spiritual one (1 Corinthians 15:44,45), He now lives in the spirit of every born-again person and is available to nourish their soul and live His life through them. Jesus paid for your sins by substituting Himself for you, then made it so He can victoriously live His life through you at all times.
I don't have much to say about verses 19,20. You can read a lot of commentaries and hear a lot of opinions about what they mean. I guess they mean what they say, and I don't know of other scripture that sheds much light on them. They're more of a segue to our second anchor, and that's baptism. Peter declared that baptism saves you! Some believe baptism is part of saving grace and works with Jesus' blood to pay for sin. Unfortunately, that contradicts sound teaching on salvation. Ephesians 2:8,9, Titus 3:5, and Romans 4:1-25 all teach that salvation is purely by faith and not any works. So in what way does baptism save you?
It's not that it washed the dirt off you, but rather that it gives you a clear conscience before God, providing salvation in every moment. With a clear conscience before God, you are anchored in the place of no guilt, doubts, or vulnerability to attack or lies because you know that you are in right standing before God, having obeyed His Word. Don't overlook that your good conscience is based on Jesus' resurrection for you, which ties the anchors together.
On the one hand, Jesus has done everything for you so that your sins are paid for and removed and you have a relationship with God for time and eternity. No one can change that in any way — it's an anchor! On the other hand, you have obeyed the Gospel and the command to be baptized, so now you have a clear and confident conscience and are impervious to any enemy attack.
Proceed with a life of obedience to God and reliance on Jesus to live His obedience in and through you in each moment. Rejoice, be strong, and live an anchored life to God's glory and for your good.