Reason #1 - There are false converts in the church.
Jesus said, "You will receive power when the Holy Spirit has come upon you, and you will be my witnesses in Jerusalem and in all Judea and Samaria, and to the end of the earth." Some professing Christians aren't sharing their faith because they aren't possessing Christians. They haven't received the Holy Spirit that dwells inside every true believer. This is foundational. The question I would ask is this, if you aren't witnessing, is it perhaps that's because you have nothing to witness about?
Here's a few quotes, brace yourself, these might sting a bit:
Charles Spurgeon said: "Have you no desire to see others saved, then you're not saved yourself. Be sure of that."
Mark Cahill said: "If you don't talk about Jesus, then maybe you don't love Him half as much as you think you do (if at all)."
Ray Comfort: "If you are not concerned about your neighbor's salvation, then I am concerned for yours."
Reason #2 - Unbelief
Do you believe Jesus when he says - "I am the way, the truth, and the life. No one comes to the Father except through me."
Is that true for the Muslim?
Is that true for the Buddhist?
Is that true for the Jesus of Jehovah’s witnesses or the Mormons?
Does theology even matter?
What about that unbelieving friend that you have who lives a really moral life?
Worldly speaking, they are a good person. They try to do the right thing. They're not perfect, but they don't cheat on their spouse, they're nice to other people, and they will even say nice things about Jesus, they're just not born again. What's going to happen to that person?
Do we believe Jesus when he spoke of the reality of Hell? Many people don't believe in eternal punishment. If you don't people that people actually go to hell - naturally it follows that you wouldn't tell them how to avoid going there.
Are the only verses that you have underlined in your Bible the ones that comfort you and make you feel good? Do you neglect those passages that might grieve you, and would therefore motivate you to go and talk to someone.
Simply ask yourself - "If I'm not sharing my faith, is it true that when it comes right down to it, I really don't believe what God has said?"
Reason #3 People already know the gospel
They've heard it. The ball is in their court. I don’t need to bring it up again. People do need to hear the gospel over and over again. That may have been the case in your life. You heard the message - nothing. You hear it again - nothin'. You hear it a third time - it's as if a light bulb goes off. Ah, I get it. It all makes sense after hearing it over and over again. Here's a lame sermon illustration. How many times does your alarm clock beep? Only once, or over and over again? 5am - beep. That's not doing anything for me. I'm sleeping right through that. No, it's beep, beep, beep, beep over and over until what? Until you do something. What's that? Reach over and smash the snooze button. Evangelism is the same way. Keep going - keep speaking. Speak and pray, speak and pray, rinse and repeat. Until they say - "Alright, that's enough." Then go into snooze mode and tell 'em you'll be back in 9 minutes.
Reason #4 We lack compassion
We're like Jonah. Jonah did not want to warn the wicked! He didn't care for the people of Nineveh. He wanted to see them perish! We need to repent of our calloused - uncaring heart. We're not willing to put ourselves out there and possibly suffer rejection for the sake of those who hang by a thread over the fires of hell.
Reason #5 Sin
Did you ever hear that expression about the Bible? This book will keep you from sin - and sin will keep you from this book. I think the same applies to evangelism. Sin will keep you from sharing your faith, and sharing your faith will keep you from sin. You'll feel like a total hypocrite to tell people about Jesus and then engage in sin. And when we go through bouts of sin in our life - the last thing we will do during that time is witness and share our faith. We need to repent today.
Reason #6 We're just too busy
Oswald J. Smith: "Oh my friends, we are loaded with countless church activities, while the real work of the church, that of evangelizing and winning the lost, is almost entirely neglected."
Reason #7 Fear
This fear takes many forms. What will people think of me? What if someone asks a question that I don't have the answer to? I'm afraid that I'm not equipped. What if I fail?
There is no simple answer here. You might be saying - yep, fear is my issue. Give me the elixir. What's the remedy for the fear of man? There is no quick fix. There's no simple answer here. The fear is real. Will people think we're strange? Yes. Will conversations get awkward? Yes. (I've been in those before - not fun.) Could people get angry with us? Perhaps. If you open your mouth about Jesus in certain parts of the world - could you be physically harmed? Yes. You could lose your head. The danger is real - the fear of man is real. So, what's the answer? The best answer I can give you is LOVE.
The 2 greatest commandments that Jesus gives to us, which all of the law and the prophets hang on is what? Love for God and love for neighbor. That's the motivation. And when we say - I just can-t do it. I can't open my mouth about Jesus to unbelievers. I know this person is lost and they are without Jesus and they are going to perish - but I can't do it. Ultimately, what you are really saying in that moment is that I won't do it because right now I am more important than this person. My reputation is more important than their destination. In that moment you are more concerned for your well-being and your comfort than you are for theirs.
I know that's a heavy hammer of truth right there. But isn't that true? Love is the answer.
"We overcome our fears through love. The Bible says that perfect love casts out all fear. Think of a firefighter. He's up a sixty-foot ladder. In front of him are a mother and two children, clinging to each other in a window on the fourth floor of a burning building. Flames are licking at the terrified family. If he doesn't rescue them, they will certainly die. Would he rather be home spending time with his wife and kids? Of course he would. But he ignores his fears and he denies himself his own legitimate pleasures because he is thinking of that family's terrible fate. Love consumes his fears." - Ray Comfort