I think they meant something even more basic, and common to all cells: you can't make a new cell without an existing living functioning cell. We have no firm id

I think they meant something even more basic, and common to all cells: you can't make a new cell without an existing living functioning cell. We have no firm idea of how the first cells developed, but all of the cells we know of today come from the division of another cell, and we have never observed anything remotely like a new cell forming pit of a puddle of all the required substances and DNA.