Lets start with a simplest observation : Looking at a tree.
How do we look at it?
How do we see it?
We see not only with sensory perception, but also with our mind. The mind creates an image of the tree and we say : 'This is a mango tree.' So our knowledge of the tree from the past, interferes with the looking at that tree at that same moment. Stating it simply, knowledge of the tree prevents us from looking at the tree because looking at the tree in core sense means being in contact with it without identifying it as a tree but observing it completely. And we cannot observe it completely if the past interferes.
Connecting it with life, we cannot enjoy our present if the past interferes. Now imagine we represent past as blue and present as red. In the color spectrum, the blue can never interfere with the way we perceive red as they have separate wave lengths. The moment we experience this fact in our life, we say 'Aha!', and the way we perceive time gets transformed completely.
We attain a state of totality with the present.