What Does It Mean to Work out My Salvation with Fear and Trembling?

https://www.godtube.com/resource/mediaplayer/ww7g6gnx.mp4;https://content.swncdn.com/godtube/2013/07/08/442676_480p_posters1.jpg;https://www.godtube.com/watch/?v=WW7G6GNX;