NOTES for Pe1 3:15
What does it mean to "sanctify God in the heart"? Perhaps it means holding within ourselves, with all our strength, faith in God's holiness, in His ultimate and absolute goodness. From this faith then flow the desire to glorify God, to thank Him, and to worship Him.
God's goodness is also the source of all our hope, all our trust. An account of our hope, then, is our witness to His goodness, His love, and therefore to Christ, His death, and His resurrection.
This witness was commanded to us by the Lord in His "Great Commission": to go into all the world and preach the Gospel to every creature, to go and make disciples of all nations. We know how to shield ourselves from this commission, for example, with Jesus' words: "Do not cast pearls before swine" (cf. Matt 7:6), silently implying that everyone we do not want to talk with is swine. The apostle Peter calls us to crawl out of that shelter and give an account to "everyone."
The words "with gentleness and reverence" are remarkable. Reverence is understandable, since we must speak about God's holiness. Foolish jokes and comparisons are plainly out of place here, although our speech should be convincing, "with salt," as the apostle Paul says. And gentleness means that we must not force our listeners to accept our testimony or lecture them from above. We can share our experience with them, the experience of the Church, but we have no right to encroach on their freedom to decide.