In 1 Peter 1:15-16, Peter said the reason a believer ought to be holy is that they were ransomed by God with the greatest price imaginable, the blood of Jesus, the perfect and spotless lamb. The second reason Peter gives for his call to holiness is that the believer has been born again (1:22-23). The believer has experienced a change in status before God, we are now his children.
Peter’s description of salvation as being “born again” is drawn from the teaching of Jesus (John 3), but is consistent with Paul’s “new creation” and adoption language. Like Paul in 1 Cor 15, Peter says that the believer has been changed fundamentally, from perishable seed but imperishable. The believer’s salvation is imperishable because it is through the “living and abiding word of God.” The “seed” that creates this new, imperishable life in the believer is the Word of God.
Peter quotes Isaiah 40:6-8, although his words echo that whole passage. The original context of Isaiah 40 was a call for the exiles to leave Babylon and return to the land, the long exile of Israel was over. Peter addressed his readers as those living in the Exile and claims to write “from Babylon” (1 Peter 5:13). The good news preached to his readers was that the exile is over and those who are born again in Jesus Christ are able to be the holy people that God desired from the beginning.
If the believer has really “tasted that the Lord is good,” then they ought to crave more and better food. When children are born, they are only able to drink milk, but they crave it so intensely that when a baby is hungry, everyone knows it! When kids are young, parents try to get them to eat new kinds of food in order to provide more nutrition than Mac and Cheese with a hotdog. Most kids will not eat stuffed mushrooms or anything that “looks weird” (unless a stranger offers it to them in a store as a “free sample”!) This is the whole Green Eggs and Ham syndrome – if you taste it you will like it (Sam I Am).
The words “Taste that the Lord is good” is an allusion to Psalm 34:8. In that psalm David describes the blessed man who has found refuge in the Lord. The one who is protected by the Lord is safe, while the oppressors (“young lions”) go hungry. Since the believer has in fact “tasted the good things of the Lord,” it is only natural that they should crave.
The believer should put away things that are not consistent with that growth. As with human children, some things do not promote healthy growth. As parents, we tell our kids to eat the broccoli and asparagus because it is healthy and they need the vitamins, and we restrict their junk food because it is just that, junk. This restriction is not because parents are mean (or are hoarding the candy for themselves), but because they want to help their children grow up healthy.
He mentions specifically “all malice and all deceit and hypocrisy and envy and all slander.” These are the sorts of things that destroy any community, but especially Christian communities. Malice (κακία) is the opposite of virtue (ἀρετή), but appears frequently in vice lists for a kind of “mean-spirited or vicious attitude” (BDAG). It appears with anger, hatred, rage, and even bitterness. It is a kind of attitude that finds fault with everything and cannot see any good at all in something.
Deceit (δόλος) is sometimes translated “underhandedness” or “treachery.” It is the word that appears in the LXX to describe the treachery of Jacob when he stole the blessing from his brother (Gen 27:35) and the treachery of Simeon and Levi when they attacked the people of Shechem. The word appears in Psalm 34:13, which may supply Peter with his list of vices in this verse.
But it does not take a major sin to stunt our growth in the Lord – simple distractions are usually more effective for destroying our growth than “malice and deceit.” Peter’s point here is that the believer is a child of God and ought to act like it. It is only natural that the believer is growing and developing in holiness.