In "Zen Mind" Suzuki says: "The true purpose is to see things as they are, to observe things as they are, and to let everything go as it goes". To see things as they are... doesn't that involve an understanding of past and future? Past and future are part of what it is... no? So my question is... if Zen is so concerned with seeing things as they are, why is it only concerned with the present? Isn't the past and future part of what it is? If your mind is in the moment, doesn't it miss the future and past?
Though I might soon sound like a stuck record, the Wild Fox Koan from The Gateless Gate is worth studying when you first become aware of these things.
Zen holds building conceptions and understanding of the world its nature and causes, -- of causation, dependent origination, etc -- distinct from a direct insight obtained by practice. A conceptual understanding is considered necessary but insufficient (and distinct from) to insight through practice, just as owning an almanac is useful in seeing the moon and planets but is not actually seeing them, and is certainly not the planets themselves. This is also a great help when understanding issues of will and agency (which are never far behind).
Conceptions of the past and future are not a part of what is: they are a part of our understanding of what is. The future will come in time or else it will not, and the past, well, you've already missed it. It's very easy to mistake the present for our understanding of it: to have a head-up-display so full of symbols and geometrical constructions that it completely obscures the view.