So, we usually think that time flows past to present to future, and that events over 'here' and 'now' are not events over 'there' and 'then'. Well, that is true in its way. But Dogen also pointed out that the past is just a memory of the mind (it was, after all, just the 'present' back then), and the future is just a dream of the mind (what future has there been yet?). In that way, 'past' and 'future' are just dreams. So, without there truly being a 'past' or 'future', what need have we even for the word 'present' (which only exists as a concept in contrast to what is -not- the present)? If we compare it a little to a 'river', it is a little like saying that there is no 'upstream' or 'downstream' or 'here' to the river, if we just see it all as a single 'just-the-river'.