"The way we lived among you…" (as Paul described it) is the foundation for sharing Christ with others. Not what you say, but what you do as you are living, as you are going, as you are being a follower of Christ 24/7, that is what lays the foundation for the gospel to be proclaimed. If your life is authentic, people will listen to your message! But if your life is inconsistent, different on Sunday than Monday, full of holes, lost people will not want what you are trying to present them!!
And that is what we are to be for others, we are to live our lives in such a way that when people look at us, they see something "Real", something "authentic", something that points them to "Him"!