In the first epistle of Saint Peter the apostle teach us that the spiritual milk is for those born of the spirit for their growth: "Like new born babies, crave pure spiritual milk, so that by it you may grow up in your salvation" 1 Peter 2:2.
The spiritual milk is the word of God, the word that comes from divine inspiration and not from human experience: "so that your faith might not rest on human wisdom, but on God's power" 1 Corinthians 2:5. The word of God is as Thomas Aquinas explains, wisdom engendered by the gift of counsel: listen (perceive with attention), meditate with intuition and inspiration, decide with discernment.
The new born babies are the new believers those who accept the wisdom of god to grow spiritually: "When the apostles in Jerusalem heard that Samaria had accepted the word of God, they sent Peter and John to Samaria. When they arrived, they prayed for the new believers there that they might received the Holy Spirit, because the Holy Spirit had not yet come on any of them; they had simply been baptized in the name of the Lord Jesus. Then Peter and John placed their hands on them, and they received the Holy Spirit." Acts 8:14-17.
Being a new believer in the Christian faith means going from a life full of sins (living according to the flesh) to a life of righteousness ("Do unto others as you would have them do unto you", Matthew 7:12). This is redemption, conversion, justification.
And what is the spiritual milk for, that is, the word of God? To be born of the spirit and receive a second childhood, the spiritual childhood, and that is, receive the Holy Spirit:
"Now there was a Pharisee,a man named Nicodemus who was a member of the Jewish ruling council. He came to Jesus at night and said: "Rabbi, we know that you are a teacher who has come from God. For no one could perform the signs you are doing if God were not with him".
Jesus replied: "Very truly I tell you, no one can see the Kingdom of God unless they are born again".
How can someone be born when they are old? Nicodemus asked.
Surely they cannot enter a second time into their mother's womb to be born!
Jesus answered: "Very truly I tell you, no one can enter the Kingdom of God unless they are born of water and the spirit. Flesh gives birth to flesh, but the Spirit gives birth to spirit. You should not be surprised at my saying: "You must be born again". The wind blows wherever it pleases. You hear its sound, but you cannot tell where it comes from or where it is going. So it is with everyone born of the spirit". John 3:1-8
God's word is progressive, uplifting, just, benevolent, compassionate, purifying; and its goal is spiritual growth for salvation. Salvation is being born again, but much more, the gifts of the holy spirit are progressive and are intended to increase the order and perfection of the universe. The purpose of human life is to increase the spiritual gifts, as is explained in the parable of the talents. Salvation is the commitment to take the word of God where it is needed to improve.
For more information, visit my profile, follow the link, and download for free my ebook.