What comes to my mind are the words of 1 Peter 3:14–15: we are to set apart Christ as holy in our hearts and always be ready to give an answer to anyone who asks us the reason for our hope, and we are to do so with gentleness and respect. God commands us to do that.
We should be sharing our faith not out of the expertise of our knowledge, but with humble dependence upon divine help. It’s not our arguments that change people’s hearts; it’s God at work through the gospel. We who are Calvinists know that we are only saved by grace, which should have a humbling effect on us as we share the gospel.
We are also to witness with prayerful dependence upon God to change people’s hearts. What comes to my mind in witnessing is John 3:8. I have a close relative I am praying God would save. This is not a theoretical question for me; it’s a personal thing. I am praying and I won’t stop praying while that person has breath. I want God to help me be a good steward of every opportunity I have to witness. Because this relative is resistant, I cling to the promises of God, and I think of John 3:8: “The wind blows where it wishes, and you hear its sound, but you do not know where it came from or where it goes.” I rejoice that the wind can reach places I can’t reach.
So, trust in the promises of God, depend upon God’s divine help, and remember, “I’m a trophy of God’s grace myself.” That should help us share the good news of Jesus Christ with gentleness and with respect.