Could there possibly be a concept of eternity? This material world is temporary and nobody can deny it. We can just observe it: things are created or born and then they are destroyed or they die. Our clothes are subject to time, worn down, days go by, everything changes. It might seem that there was just one creation and then everything will be finished, and that's it. Nothing was before and nothing will be after.
So it is not even theoretically possible that there is such a thing as eternity.
But what about this: you have a tree which gives 10 apples; 10 apples give 10 seeds which means possibly 10 new trees; each tree gives another 10 apples and each apple gives 10 seeds, etc. There is potential for this to happen unlimitedly. How come there was nothing, then there is something and then after there will be again nothing? Does it mean that everything is just now? Do you remember many things which happened before but you don't remember them? Does then it mean they never happened or they never existed? Or if everything is temporary, then your statement also has temporary validity. So what's the meaning of your statement? It's not true, it's just temporarily true, which means it's not true at all. If you want to establish this statement as true it must be true eternally, so it can be applied. But then you must admit eternity so your statement about temporary existence can come into validity. But then that would completely disprove the validity of the statement about temporary existence. So what do you think: is eternity possible?
From the Vedas, the ancient scriptures containing the Absolute truth, describe two natures: eternal (sat) and temporary (asat). The spiritual world is eternal and material is temporary. The simplest and most frequently mentioned example is with the body; the body is changing constantly, so that is temporary. Also the mind, intelligence and ego or identification of “who am I”. But the observer never changes, since we were babies up until old age. The "I" is always there. You are always conscious and you observe all the changes of the body. Because the observer is the soul which is eternal. In the past you were existing, you exist also now and you will exist in the future, but body will be always different. Therefore by this simple observation we can see that there are two different natures: temporary and eternal.