Doing good to the people around us is essential for the Christian because the Lord God in Jesus Christ has done good to us (though we did not deserve it). This principle is true even (and especially!) in the face of ridicule. An unbelieving community may interpret doing good in response to ridicule as a sign of weakness, and the Christian may be very tempted to take matters into his own hands to set the oppressor in his place. But vengeance belongs to the Lord (Deuteronomy 32:35), and the Christian is so precious to God that he gave his only Son for him (John 3:16), and so the Christian need not fear his oppressor but trust that the Lord will provide relief and justice in his time and sustain in the meantime (Romans 8:32).
Doing good in the face of ridicule has a purpose: to invite the oppressor to ask why the Christian continues to do good to those who do him harm. This has been a theme in Peter’s writing since 1 Peter 2:11, that is, that the unbelievers of town may be prompted to glorify God (see 1 Peter 2:12; 1 Peter 3:1). In the present paragraph, Peter catches the same thought with the reference to them being put to shame.
16 having a good conscience, so that, when you are slandered, those who revile your good behavior in Christ may be put to shame.