I get what you're saying and it clarifies the concept but it feels too restrictive for me.
Doesn't everything exist within the moment? There is no past, future, in the linear sense, everything is now. The concept of 'now' allows me to understand how I am able to percieve what appear to be past and future events now because they are all happening simulataneously. Because of the time constraints of our human perception we track life in linear fashion. Our lives appear to travel along a continuum that allows us to track ourselves and events. Tolle's 'Now' theory expands the mind beyond the constraints of our physicality where as the 'Container' theory appears to restrict it.