Peter is saying that Christ's followers should not be surprised or shocked about persecution, trials, and sufferings. Being a Christian does not make us immune to suffering. Persecution for the sake of Christ and His Gospel is not a strange thing. We should expect it and be prepared for it. "In fact, everyone who wants to live a godly life in Christ Jesus will be persecuted." (2 Timothy 3:12) Jesus says in John 15:18, 20, "If the world hates you, keep in mind that it hated Me first...Remember what I told you: 'A servant is not greater than his master.' If they persecuted Me, they will persecute you also." The fiery ordeal/trial has its purpose. It tests us, refines us, and strengthens us. The pressure of affliction brings out what's really on the inside of us. How we respond to trials reveals whether our faith is authentic.
"God's love for His Son was never a shield To keep Him from Calvary's cross; God's love for His children demands that we yield To trials that burn out the dross." (Gustafson)
Not only we should expect persecution, but we also should rejoice through it. Stay joyful. "Consider it pure joy, my brothers and sisters, whenever you face trials of many kinds, because you know that the testing of your faith produces perseverance. Let perseverance finish its work so that you may be mature and complete, not lacking anything." (James 1:2-4) Choose joy. Don't let adversity rob you of your joy. True joy does not depend on circumstances, but on God. Circumstances change but God never changes. We rejoice even in the furnace of trials because we know and value their purifying effect and we know and value the presence of Christ with us. "When you walk through the fire, you will not be burned; the flames will not set you ablaze. For I am the Lord your God, the Holy One of Israel, your Savior...Do not be afraid, for I am with you." (Isaiah 43:2b-3, 5a) Peter encourages Christians to look ahead to the future when all their suffering will be transformed into glory in Heaven. Our trials will some day be over and our joy will be forevermore. Rejoice even now in that truth. "Now if we are children, then we are heirs--heirs of God and co-heirs with Christ, if indeed we share in His sufferings in order that we may also share in His glory. I consider that our present sufferings are not worth comparing with the glory that will be revealed in us." (Romans 8:17-18) Because of our spiritual union with Christ, we share in His sufferings and He does in ours. As we suffer with Him and for Him, we will be glorified with Him. Beloved, keep on rejoicing now in suffering for Christ since it's an honor & privilege in order that you will be overjoyed at the revelation of His glory for you will also share in His glory. No pain, no gain. No suffering, no glory.
"The apostles left the Sanhedrin, rejoicing because they had been counted worthy of suffering disgrace for the Name. Day after day, in the temple courts and from house to house, they never stopped teaching and proclaiming the Good News that Jesus is the Messiah." (Acts 5:41)