many complex systems are synergistically greater than the sum of their parts. That synergistic additional something that makes us human, more than our skin and bones - it is immaterial inasmuch as we do not find it between the cells; but it arises from our material existence. We exert influence beyond our own lives due to our interactions with Culture - another immaterial manifestation of the collective actions of many components (many humans making a culture, whereas many cells make a human).
This immaterial "humanity" we each manifest, it is a unique attribute of our individual existence. We each live in our own unique place and time and we each have our own unique imprint on the rest of humanity. That imprint, great or small, is indelible. It has local effects which may not be apparent long after we are gone, but in the time of our living and some time after it persists.
Time is a dimension of spacetime. It appears from consideration of the consequences of General Relativity that time, like the spatial dimensions; is "complete". All the points of space exist in a permanent way, regardless of whether we are present to observe. Likewise, it seems likely that all the moments of time are permanent. The vast four-dimensional universe of spacetime is complete from here to infinite reaches of distance and from beginning to end. Our thread of existence - moving here and there in space over an allotted span of years - is a permanent and eternal aspect of the universe; a thread in the great tapestry of existence. Vital to the overall beauty of the whole.
Despite that spacetime is complete, it is clear that events are linked by causality. We are agents of causality - we somehow create the future that already exists. This is an enigma. Although we probably cannot physically change the course of our existence, it certainly feels like we can. I choose to type these words, or not. There is no "going back" and existing in a different way, so we cannot empirically demonstrate the existence of real choice; only sense it. To the extent that such choice is real, I think I am making the best choices for a happier world. But in fact, I may simply be experiencing the path of an eternal thread no more changable than the eternal motions of the galaxies.