Do all souls start out on the physical plane? The reason I ask this is that I am curious where such spirits as angels and demons fit into this equation. Are there spirits that simply start out in the astral plane?
On a related note, is it common to receive glimpses of one’s previous life in the astral before our current physical life? I felt like I had a brief glimpse of the very end of my last astral life before coming into this physical body, and it has had a big impact on me.
All souls start out as part of God, as one with the Spirit beyond creation. It is said that God created all the universes, causal, astral, and physical out of Himself. This means that we, as souls, are part of Him. That is why we can truly say, we are children of light and not darkness.
This is a fascinating and complex subject. I would highly recommend that you obtain a copy of The Essence of the Bhagavad Gita. Beginning on page 307 of the hardback edition there is a detailed description of what you are asking about and how it all fits together.
And for the second part of your question, it becomes more common to remember one’s past lives as you meditate regularly and become less identified with your present lifetime as being your only one. All of this is a process, but a natural one that occurs as you engage regularly, seriously, and deeply in the spiritual life.
Again, I have found The Essence of the Bhagavad Gita very helpful in providing explanations of these deep and profound questions that naturally arise.