The call to holiness begins with (and is about) our relationship with God--a vertical atonement in which God draws near to us and we draw near to Him, and then its horizontal application to our everday lives.
Whatever is inside of us is what comes out of us. If we have discontent, bitterness, hurt... that's what we'll give others. If we're drifting off course or allowing the world to fill us, that's all we'll be able to offer, because our horizontal relationship is an expression of our vertical relationship. If the vertical is out of whack, so is our witness to the world.