Following I Peter 2:1, in which he admonishes us to rid ourselves of the fruits of spiritual junk food, Peter lists evidence of a mind afflicted with a poor spiritual diet. Malice is ill will, the desire to inflict pain. Deceit is lying or crafty, seductive, and slanderous activity. Hypocrisy is pretending to be what one is not. Envy is the strong desire to possess what belongs to another. Evil speaking is using the tongue to gossip, deceive others, or destroy reputations.
Peter proceeds to encourage us to crave God's Word just as a baby craves milk. He is not encouraging us to desire elementary spiritual food but emphasizing the energy we should exert to get good spiritual food. Babies demand milk as if their very life hangs in the balance at each feeding.
The apostle calls God's Word pure, meaning uncontaminated, unpolluted by fraud or deceit. God's Word is truth (John 17:17). David says that God's Word is refined seven times (Psalm 12:6). Truly, Peter is teaching us that God's Word promotes spiritual growth and good health just as good food can do physically.
In using milk as a metaphor, Peter is in no way chiding people as Paul does in Hebrews 5:12-14. The former uses milk simply as a nourishing food because his emphasis is on desire, not depth. Paul uses milk as a metaphor for elementary because he wants to shock the Hebrews into comprehending how far they had slipped from their former state of conversion.