Peter was writing to new believers that were scattered throughout the area that is roughly today the nation of Turkey. Many of these people have come to Christ through Paul’s church planting work and now Peter is calling them to continue to grow in their faith.
In chapter 2, Peter says:
Like newborn babies, crave pure spiritual milk, so that by it you may grow up in your salvation, now that you have tasted that the Lord is good.
1 Peter 2:2-3
What is it that Peter is saying when he says that these new babies should “grow up” in their salvation? Growing up, in a spiritual context, would refer to a few different things:
Righteousness: First and foremost, growing up means growing in righteousness. We have been reborn and made into a new creation, so we leave behind our old life of sin and live a life of righteousness. This is the first meaning of growing up.
Produce fruit of the Holy Spirit: Instead of producing fruit of the flesh, we begin to produce fruit of the Holy Spirit. Growing up in our salvation means to preemptively act in ways that accord with the fruits of the Spirit.
Produce fruit in the Kingdom of God: We look for ways to see the Kingdom expand. We make disciples of Jesus. We equip others to do good works. This produces more fruit.
In this particular case, Peter says that the people should crave pure spiritual milk. Very simply, Peter is saying that the people need to take their first steps in growing in their relationship with Christ. Peter is saying that this isn’t a simple “transaction” where the people were saved and now can just go on living their lives as they did before. No. Instead, he is calling them to growth, to become mature, to live as people who are growing beyond their infancy into maturity to adulthood.