We should not understand the heart as our inner and private lives, which are inaccessible to others. The heart is the origin of human behavior (cf. 1:22; 3:4), and from it flows everything people do. Hence, setting apart Christ as Lord in the heart is not merely a private reality but will be evident to all when believers suffer for their faith. The inner and outer life are inseparable, for what happens within will inevitably be displayed to all, especially when one suffers.
The exhortation here is instructive, for Peter assumed that believers have solid intellectual grounds for believing the gospel. The truth of the gospel is a public truth that can be defended in the public arena. This does not mean, of course, that every Christian is to be a highly skilled apologist for the faith.244 It does mean that every believer should grasp the essentials of the faith and should have the ability to explain to others why they think the Christian faith is true.
the Christian is never to evade or to put him off, he is to be ready to present his case, his defense, to render account as to what his hope embraces, and as to why he holds it in his heart. We may say that he is to be ready always to testify, to correct ignorance about Christ, to spread the gospel light, to win others for Christ, to justify his own hope, and as Peter adds here (v. 16), to silence evil speakers with his good conduct which certainly speaks for itself and puts slander to shame.