Time outside this subjective 3 dimension world, is not linear like an arrow. Time is more like a landscape with zones. Each zone is a different frequency which can be accessed with our higher consciousness. This is why they are really 'co' lives not 'past' in a true sense. It is a bit like going on a train, and seeing the stations in a linear fashion because of a time table schedule. We see them one by one through the frame of our window but the stations are all existing independently of the time table. They were there before we arrived and will not cease to exist when we have gone.
Quantum physics tells us about parallel worlds and even universes. There are many 'earths' each in it's own cocoon of reality, quite independent of each other and quite unaware of the existence of others like themselves.
We each have many existences on these other dimensions as well as this one. We live in cycles of lives, each fulfilling a required task, lessons with an obstacle/test put in, and enabling our soul to develop as we learn those lessons through our experiences, that we enable us eventually, to return to our Source as Perfected beings, able ourselves to aid in Creation. It is as if our Soul is like a Crystal or Diamond and each life is a separate facet of that diamond. We need all facets to be developed so that our Soul is beautiful.
In Past (Co) Lives recall we try to access these other dimensions of our Soul through our Higher Consciousness, and seek the reasons why we are in this life and why certain relationships are as they are. This is done on a One-to-One basis with Ruth for safety reasons. Ruth can also tune into your other lives for you. On our own we may get into mental/psychic situations which could cause us problems. We need an experienced guide.
These incarnations/lives are facets of our Spiritual Diamond.