I've been reading Richard Wurmbrand's Tortured for Christ, a book about the sufferings of Christians under the Communists, particularly Wurmbrand's own suffering in Romania. This book puts some flesh and bones on what we read about suffering in 1 Peter, enabling us to see with our own "eyes" the reality of the unique role suffering plays in our purpose as Christians.
In 1 Peter 2:9-10 we read:
But you are a chosen race, a royal priesthood, a holy nation, a people for God's own possession, so that you may proclaim the excellencies of Him who has called you out of darkness into His marvelous light; for you once were not a people, but now you are the people of God; you had not received mercy, but now you have received mercy.
God calls and saves a people for Himself for the purpose of "proclaiming His excellencies"—the pinnacle of those excellencies being His mercy and grace that changed us, His enemies, into His people. And in 1 Peter, we find two ways that suffering accomplishes this purpose. The first is in 1:6-7:
[Y]ou have been distressed by various trials, so that the proof of your faith, being more precious than gold which is perishable, even though tested by fire, may be found to result in praise and glory and honor at the revelation of Jesus Christ.
The truth about Christ's death on the cross for our sins, about our adoption as God's children, and our future enjoyment of Father, Son, and Holy Spirit forever is something far more precious than gold. And every time a Christian endures suffering and holds on to this truth instead of giving up in unbelief, cynicism, or bitterness, he is revealing God's glory to the world by saying the height of God's value is even greater than the depth of pain in suffering. In the case of Wurmbrand and his fellow prisoners, this is saying something indeed.
But there's yet another way suffering accomplishes God's purpose for us. Peter twice couples our suffering with a description of Christ's suffering. First in 2:21-24:
For what credit is there if, when you sin and are harshly treated, you endure it with patience? But if when you do what is right and suffer for it you patiently endure it, this finds favor with God.
For you have been called for this purpose, since Christ also suffered for you, leaving you an example for you to follow in His steps, who committed no sin, nor was any deceit found in His mouth; and while being reviled, He did not revile in return; while suffering, He uttered no threats, but kept entrusting Himself to Him who judges righteously; and He Himself bore our sins in His body on the cross, so that we might die to sin and live to righteousness; for by His wounds you were healed.
And again in 3:17-18:
For it is better, if God should will it so, that you suffer for doing what is right rather than for doing what is wrong. For Christ also died for sins once 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.
When we suffer unjustly and respond as Christ did, we serve as a picture of Christ to our persecutors and to the world, proclaiming His glory and revealing Him to those who don’t yet know Him.
Wurmbrand and his fellow Christian prisoners would suffer through their beatings, refusing to deny Christ, and then turn and pray in love for those tormentors whose sin was responsible for the cruel destruction of their bodies. By this living illustration of the beauty of Christ's character, work, and value, some of the guards saw Jesus for the first time and became His followers.
The suffering of Christians, inevitable and expected, uniquely accomplishes both of these goods in the service of our ultimate purpose of glorifying God and His grace.