What does it mean: Like newborn babies, crave pure spiritual milk, so that by it you may grow up in your salvation", in the bible
The apostle Peter in 1 Peter 2:2, refers to the Word of God as "pure (unadulterated) spiritual milk": Like newborn babies, crave pure spiritual milk, so that by it you may grow up in your salvation".
Milk is a food par excellence for children, and spiritual milk is food par excellence for the spirit of man, and this is the Word of God. The Word of God is the knowledge of the correct means to live, the Word is eternal and uncreated, the Word is, as Thomas Aquinas explains, "engendered wisdom", that is to say, it is all that wisdom that arises from the spiritual gift of Advice: perceive with Attention, meditate with intuition and inspiration, decide with discernment.
But also this spiritual milk must be "unadulterated"; What does Peter mean? It refers to the fact that it should not be adulterated by heresies (error teaching) and sophisms (knowledge with the appearance of philosophy, but it is not). Examples of heresy in the gospels are the Law of Talion: "an eye for an eye, a tooth for a tooth" (Matthew 5:38), "love your neighbor and hate your enemy" (Matthew 5:43). This Word is addressed to spiritual children who must drink the "pure (unadulterated) spiritual milk", when Peter speaks to us of newborn children he speaks to us of those who have received a new spiritual childhood, in philosophy this birth is called "Gnosis" (knowledge), there is a birth of the flesh and a birth of the spirit (progressive mentality), as explained or described by Jesus to Nicodemus:
"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
In this birth of the spirit as Jesus describes it, we receive the same essence of God, the wisdom, to achieve a full likeness to God; the rational or soulish man, in whom the soul prevails (philia), becomes a spiritual man, that is to say, the man in whom the spirit prevails (Agape), in order to carry out the plan of salvation.