Get this straight. I don’t want you to convert me to your particular brand of Christianity. I don’t want to hear about your personal relationship with God. I have my own. I don’t want you to hand me a tract filled with Bible passages. If I want to read the Bible, I will. I don’t need you to tell me which parts should be important to me. I don’t need your help or your guidance in any way.
I will, however, be civil so long as you are, and will dismiss you politely, despite any irritation I might feel. I can tolerate these minor intrusions into my personal life. Well, most of the time.
To witness is to observe. To tell about what one has witnessed is to testify. When you tell me about how you found God, you are testifying, not witnessing. I can tolerate the former, but the latter really pisses me off.
If you are going to try to change my deeply held personal religious beliefs, the least you can use the proper diction while you do. You won’t change my mind, but you are a lot less likely to be assaulted in the process. Why take the chance?