So retention is a mode of givenness, but it is a primordial mode, i.e., the first, only and originary way the past as such is given. Through retention, the past is given itself in person. It is not that something else is given that represents or reminds us of the past, something which can be compared to, or corresponds with, or symbolizes that moment in the past. That would be to have the past or its representative present as a now.
The past itself is given to us; it is not mediated by something else which stands for it or corresponds with the prior reality. This would make the past itself inaccessible; if this were the case, how could we ever know if the representative faithfully represented the past itself, since it would then be inaccessible? Retention is the mode of consciousness by which the past is presented, not represented.
In Husserl's own words, "if we call perception the act in which all 'origination' lies, which constitutes originarily, then [retention] is perception. For only in [retention] do we see what is past; only in it is the past constituted, i.e., not in a representative but in a presentative way. It is the essence of [retention] to bring this new and unique moment to primary, direct intuition, just as it is the essence of the perception of the now to bring the now directly to intuition." (Husserl, Internal Time Consciousness, p.64)