The new life in Christ has ethical ramifications. Being born again means that you should cast off certain behaviors and earnestly seek God’s righteousness. This is the two-faceted exhortation which begins 1 Peter 2.
On the one hand, those who have been given new and everlasting life by the word of God must, “Therefore, rid yourselves of all malice and all deceit, hypocrisy, envy, and slander of every kind” (1 Pet. 2:1). Like other NT ‘vice lists’ this is a representative group, not exhaustive–that is, the apostle surely would want believers to throw off greed and lust as well, though he doesn’t mention them. It is also a list that focuses more on the attitudes of the heart than on the external actions that emerge from these attitudes. And it is a list of sins that particularly would disrupt the brotherly love that Peter has called for Christians to show one another.
But Christian ethics isn’t just about what you cast off; it’s also about what you take on. “Like newborn babies, crave pure spiritual milk, so that by it you may grow up in your salvation, now that you have tasted that the Lord is good” (vv.2-3). The sinful attitudes of the heart are to be replaced with the goodness of God, with His Word and the spiritual growth brought by the Spirit. Peter is not suggesting here that the believers he’s writing to are immature, but he’s using the image of the new birth to urge believers to seek spiritual growth as earnestly as babies crave the milk that helps them grow.
All of this is predicated upon the work of God in the life of the Christian. God is good, the source of all goodness and life. You have tasted God’s goodness; let that taste drive you to more and more fulness in Him.