flowerbudh wrote:...I don't believe it's existence came out of non-existense.
This is a philosophical point in Buddhist thinking. For anything to be 100% existing or non-existing is not possible because 100% existing would mean that it could be independent and unchanging - it would be "outside" the cosmos.
So you are right to mention change, and in fact everything can change because it can interact with other "things", but it is only in our mental classification that we draw lines around things and call them separate, beyond which they are already connected.
So we have two different perspectives to consider. This wooden table I am using changes very slowly and for me, it serves as an unchanging table - i.e. it has the identity of the thing called "table" - but if we take a wider perspective, it was once a tree, and before that it was just a seed, and in the future it will disintegrate in some way, so its essence is to change even though it appears solid right now.
If we trace back to what the table/tree is actually made of - it took the seed from its parent tree, sunlight, water, carbon dioxide, and the idea of the person who made it, etc. and all those things had to come together in a very specific way to make it - there is nothing solid we can grasp onto to identify what it actually is other than a series of processes, except by drawing a mental line somewhere and artificially isolating certain aspects.
As a result, it is almost impossible for us to "think" at the level at which things actually "exist" - in order to think at all, we need to classify and categorise in order to make any sense of the world whatsoever - our "sense-making" faculties are always a distortion of one kind or other.
So even your question, "what is "passed" karmically from one life to the next" is based on the idea of a boundary between lives, based upon the way things appear to us and the way we mentally categorise the universe, rather than what actually occurs - an endless flow of changing processes.
Then we encounter another problem with perspective, because the idea of "an endless flow of changing processes" only applies when we are ourselves a part of that. Yes, we can imagine what it might look like if we could take a step away from it, but if we actually were to step out of that flow, then we would have no perception of it at all, we would literally be outside of time and space.
(I realise this isn't in itself an answer, but in some ways it is more important how we lay out the problem. I would suspect any simple answer involving another level of "Being" would either replicate the same issues at that level or close them off by reference to the imaginary.)