It's true some people don't believe in God, but it's much more likely for someone to doubt than disbelieve. After all, the creation blares all day long, "There is a God." Someone would have to be profoundly un-inquisitive to actually disbelieve.
For this reason, our witnessing (and apologetics) effectiveness will go up a notch if we focus less on proving the existence of God and more of demonstrating His love. It was, after all, for "love" that Jesus created the world and reduced Himself to human flesh for a season.
It's not, "And all men will know you are my disciples if you perfect your theology." (Though you should). Of course we need to make the intellectual case. People need to have the right information. But a genuine example of God's love is much more compelling. Truth clears the path, but it is His agape that converts.
Until every church disciples every man...