That’s a great question, and there is a real answer. In the book of Matthew in the New Testament, Jesus was getting ready to go back to heaven and said this: “All authority has been given to Me in heaven and on earth. Go therefore and make disciples of all the nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, teaching them to observe all things that I have commanded you; and lo, I am with you always, even to the end of the age.” (Matt. 28:18-20) After that, the rest of the New Testament pretty much involves going out and doing that.
Not all religions or belief systems are like this, and the tension between groups who regularly share their faith with those who don’t (or don’t want to hear anything about anyone else’s faith) can be confusing or irritating. It’s a little like the Americans and the French. One of the best things I ever read about the love/hate relationship between these two countries is that while most countries enjoy their culture, only the Americans and the French deeply believe that theirs is simply the best, and all other cultures are either a (pale) variation on their culture, or different in a worse way. That’s why we bump heads all the time, apparently. And if we each feel that way, there will always be some tension.
It’s a part of genuine Christianity to share what we know, and what we have experienced. We are quite aware that many folks don’t believe that, and don’t want to hear about it. But since we believe that Christianity is the One Truth, we feel it applies to everyone in every age in every culture. Most of us are very grateful to God for what He’s done in our lives, and we like to share good news. We deeply believe that God has a plan for everyone, and that everyone needs Him. But more important than even that is that Jesus told us to do it, so we do.