In 1 Peter 2 the apostle Peter tells us that we are like bricks (or stones) being fit together to build a house. The metaphor here is that followers of Christ fit together to form a complete structure. Placed together properly, the whole is greater than the sum of its parts.
As you come to him, a living stone rejected by men but in the sight of God chosen and precious, you yourselves like living stones are being built up as a spiritual house, to be a holy priesthood, to offer spiritual sacrifices acceptable to God through Jesus Christ.
1 Peter 2:4-5 (ESV)
Peter is telling the church that each person contributes to the overall support of the building. Like any structure, a missing brick here or there, while unsightly and certainly deficient, probably wouldn't cause the building to collapse. But remove enough and a point will come in which the building will simply not be able to stand and serve its purpose.
The key point here is that while Peter is talking to the church as a whole, he's not diminishing the role of each, individual person within it. And even more, he's establishing a principle that many people struggle with: God does have a place--or rather, function--for each, individual person. Notice Peter doesn't address where each, individual stone is placed. That's not a job for people; that's a job for God. Peter instead focuses on the purpose of the combined whole: to be a holy priesthood and offer spiritual sacrifices.
Peter originally wrote this letter to followers of Christ who were facing hostility as a result of their faith. It's interesting that Peter chose this moment to remind Christians that everyone is included, valued, and even, needed. It would be easy for these people to think back to all the miracles that Jesus and his followers did and wonder why they, themselves, were experiencing adversity (and some, likely, death). Peter's response is a reminder that they each have been chosen to be a part of something greater--something that spans not only this lifetime, but beyond. Therefore, they should stay focused and determine to live their lives accordingly.
So he came again to Cana in Galilee, where he had made the water wine. And at Capernaum there was an official whose son was ill. When this man heard that Jesus had come from Judea to Galilee, he went to him and asked him to come down and heal his son, for he was at the point of death. So Jesus said to him, "Unless you see signs and wonders you will not believe." The official said to him, "Sir, come down before my child dies." Jesus said to him, "Go; your son will live." The man believed the word that Jesus spoke to him and went on his way. As he was going down, his servants met him and told him that his son was recovering. So he asked them the hour when he began to get better, and they said to him, "Yesterday at the seventh hour the fever left him." The father knew that was the hour when Jesus had said to him, "Your son will live." And he himself believed, and all his household.
John 4:46-53 (ESV)
While seemingly unrelated, the child in this passage is representative of the physical struggle and adversity experienced by the recipients of Peter's letter. Just like the son was at the point of death, so to were those Christians. Yet Jesus's intervention changed the trajectory of the son. Where he was once sentenced to only sickness and death, now he had been given a new lease on life. Before he would have struggled to accomplish anything because he was bedridden, now he was free to fulfill his function. Earlier his condition paralyzed friends and family who were concerned with his well being, now they were able to continue. The passage in 1 Peter 2 reminds followers of Christ that their life is valued and required; it makes a difference in God's plan if they are included.
Sometimes the specific role or function of an individual is unclear. It's difficult to look at one brick on a house and think that brick contributes; yet it would be obvious when looking at the house if that one brick were removed or misplaced. God doesn't just want us, God needs us to be included. He could have done anything on His own but chose to include individuals in His plan because He values each person and wants each person to recognize this through their contribution to His purposes.