I Peter 2:12 Be careful how you live among your unbelieving neighbors. Even if they accuse you of doing wrong, they will see your honorable behavior, and they will believe and give honor to God when he comes to judge the world.
How careful are you with how you live amongst men? Do you say one thing but teach something else by how you live? Are you acting and reacting around others in such a way that they know Christ makes a difference in you? Non-believers are not stupid. They can spot phony believers pretty easily. They know whether or not Christ has changed us. If they see in us things that don't match up to what we preach and teach, they will more than likely not listen to us. The world generally pays little attention to the Christian message because they don't see it at work like we say it does.
When we live honorable lives before God and man, people will notice. They may not accept what we say with their minds, but they have to accept it with their hearts. Deep down they will know that we are who they would like to be. When the world sees the Gospel working like it is supposed to be, they will respect us, even when they don't agree with us and oppose us.
Strive to live in such a way that the world cannot refute the difference Christ makes in you. Practice what you preach. Be as consistent as possible in your application of Biblical truth. Don't give others an excuse to reject the Gospel because of what they see in you. Instead, give them a reason to embrace it because of how they see it at work in you.