You ever hear the saying, "Your true character is who you are when nobody else is around?" I believe that statement is very accurate. It's easy to appear one way to somebody or a group of people and then act entirely different when we're by ourselves.
A very common problem that a lot of Christians face is this; they have no problem acting like a die hard - true hearted Christian when others are around, but when they're alone, they tend to not act/think like a Christian at all. We need to work hard at not letting this happen in our lives.
If we are displaying to others that we have Christ in our lives, we need to be true to that - at all times (not just around others). We need to closely keep ourselves in check when we're alone to make sure our hearts and minds are staying true to God.
Our hearts reveal who we are - we need to have a heart that is on fire for God.