Time present and time pastFull. Stop. All the rest of the Four Quartets discuss the alternative hypothesis.
Are both perhaps present in time future,
And time future contained in time past.
If all time is eternally present
All time is unredeemable.
But first the discarded hypothesis. Perhaps time is a dimension like space. Perhaps the past and the future are just as 'present' as the present, perhaps other times are like other places, which exist in a definite fixed form. Perhaps the past and the present and the future are implicit each in each other. Perhaps by knowing the present we have sure knowledge of the past and future. Perhaps the past is not burnt.
If this hypothesis is true - argues Eliot - there is no free will, there is nothing to be attempted. No hope. Time is unredeemable. This whole world is a total mockery.
But if this hypothesis is wrong, then our existence in time is much more complex, and difficult, but also meaningful and hopeful. And the rest of the poem, and the four poems, are about the implications of that.