We are but a spec of dust which only exists in one moment in the progression of time. In our present time, on our spec of dust called Earth, we are but one spec of dust among a population of over seven billion other specs of dusts called humans. We are insignificant not only in time and space, but also among the more than seven billion other specs on this Earth. Each of us came from dust, are dust, and will return to dust.
All our efforts are worthless not only in the vastness of time and space, but also among the other seven billion humans on this planet. Our actions have little to no effect on the lives of most of these humans. Through the course of a life we may have some small impact on the handful of humans close to us, but most of us have no effect on the billions of other humans past, present, and future.
Christianity teaches us that we have value for one reason only. Our value is only derived from being created in the image of the Triune God. We only have value in that we are an image of the creator of time and space. Every one of those seven billion specs of dust, as well as all the specs of dust before us, have been created in the image of the Triune God. It is our creation that provides value and significance.