Jamieson, Fausset and Brown on 1 Peter 3:16

16. Having a good conscience--the secret spring of readiness to give account of our hope. So hope and good conscience go together in Ac 24:15, 16. Profession without practice has no weight. But those who have a good conscience can afford to give an account of their hope "with meekness."

whereas--(1Pe 2:12).

they speak evil of you, as of evildoers--One oldest manuscript reads, "ye are spoken against," omitting the rest.

falsely accuse--"calumniate"; the Greek expresses malice shown in deeds as well as in words. It is translated, "despitefully use," Mt 5:44; Lu 6:28.

conversation--life, conduct.

in Christ--who is the very element of your life as Christians. "In Christ" defines "good." It is your good walk as Christians, not as citizens, that calls forth malice (1Pe 4:4, 5, 14).