Peter speaks of his readers as if they were babies. Babies requires very pure food, which they can digest easily. In the same way, believers need pure teaching from God's word. Alternate translation: "Just as babies long for their mother's breast milk, so you must yearn for pure spiritual milk" (See: [[rc://en/ta/man/translate/figs-metaphor]])
Here the word "salvation" refers to when God brings the salvation of his people to completion when Jesus returns (see [1 Peter 1:5](../01/03.md)). They were to increasingly act in ways that were consistent with this salvation. You can translate this with a verbal phrase. Alternate translation: "you may grow up spiritually until God saves you completely" (See: [[rc://en/ta/man/translate/figs-abstractnouns]] and [[rc://en/ta/man/translate/figs-explicit]])
Peter speaks of believers advancing in knowledge of God and faithfulness to him as if they were children growing up. (See: [[rc://en/ta/man/translate/figs-metaphor]])