"Others, like seed sown on rocky places, hear the word and at once receive it with joy. But since they have no root, they last only a short time. When trouble or persecution comes because of the word, they quickly fall away." – Mark 4:16-17 (NIV)
My Thoughts: I have seen that. It's weird how people can be so die-hard and committed and talkative and sharing about certain things one minute and the next it's like they forget it and move on and never mention it again. I think it has to do with grasping a brief glimpse of truth and meaning but then not letting it really sink in and become a part of your life. You preach about God and talk about him a lot, but you don't bring Him into your life and He still seems like a concept to you.
I have a few friends that a re like that. It kind of frustrates me sometimes because they'll use Christianity kind of like a hallmark moment for themselves -often to judge others -but they aren't really spiritual and don't try to extend grace to others.