No, this is not the title of a Chronicles of Narnia book, but the three descriptors that Peter calls his audience in 1 Peter 2:1-10. Each one will shed light on a different aspect of a Christ follower, yet they fit together very nicely.
Like newborn infants, long for the pure spiritual milk, that by it you may grow up into salvation—if indeed you have tasted that the Lord is good. 1 Peter 2:2-3
First, to clarify what Peter is saying, he is not calling the readers new Christians necessarily, like he did in 1 Corinthians 3. Rather mimic what babies do and crave which gives them sustenance. Our spiritual milk is the Word of the Lord. Instead of pursuing malice, deceit, hypocrisy, envy and slander (v.1) pursue the Word. To “long for" is a strong expression that we could paraphrase "develop an appetite for.” The outcome for our perusal of God’s Word is our salvation. Salvation here, as Peter used previously, refers to the full extent of salvation that God desires every Christian to experience.
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
God is not only the source of sustenance, but also becomes our foundation. He is the living stone, the corner stone that we are being built upon. I am amazed that this passage tells us we are like Christ in the fact that we are also living stones. We have been baptized into Christ, and we share in the inheritance of Christ as children of God. However, there is a great distinction in that Christ is the cornerstone that we are being built upon. This passage pictures a house being built by each new believer who become living stones. Each Christian is an essential part of the body and mission of Christ.
A Choose Race
But you are a chosen race, a royal priesthood, a holy nation, a people for his own possession, that you may proclaim the excellencies of him who called you out of darkness into his marvelous light. Once you were not a people, but now you are God's people; once you had not received mercy, but now you have received mercy. 1 Peter 2:9-10
God’s chosen race in the Old Testament was the nation of Israel. The mark that Israel was God’s chosen race was the fact that He dwelt among them (Ex. 19:5). He did this in the tabernacle and the temple, until the abandonment of the Israelites made this intimacy impossible. Then the presence of God departed from His people (Ezk. 10). Now, in the church, God does not dwell among us, but resides inside of us (John 14:17; Rom. 8:9). This is the mark that we are his chosen people. As His chosen people, we carry out His mission by being lights that shine on those who still are in Spiritual darkness.
As Christians we are babies, stones, and a chosen race. These are not merely descriptors, but qualifiers. We are to seek the Word of God as our daily nourishment in order to come together as the the church is supposed to be, one unified vessel, so that we may accomplish the work of Christ. Peter here is continuing to clarify our identity and mission as follower of Christ.