This curtain/veil stuff separating us from the spirit world has, to me, always smacked of US Spiritualism and the vestiges of ancient pagan (Celtic I believe) myths.
The first example that comes to my mind is when you’re with someone who’s in the process of passing away. Sometimes, it smacks you like, “Woah, this feels like childbirth” and sometimes, it smacks you like, “Woah, this is a thin place.” But if you’ve felt a thin place, you know what I’m trying to describe.
“Beyond the veil” is a phrase that originated in the Bible. Because it refers to-- the Veil that separates the Holy of Holies from the rest of the Temple, and eventually evolved into a phrase meaning to show the separation between the ordinary and material, and the holy and the unknown.
Having therefore, brethren, a confidence in the entering into the holies by the blood of Christ;
A new and living way which he hath dedicated for us through the veil, that is to say, his flesh,
And a high priest over the house of God:
Let us draw near with a true heart in fulness of faith, having our hearts sprinkled from an evil conscience, and our bodies washed with clean water.
A curtain or veil is a good word for it— it’s just a thin sheet of almost-nothing that keeps us from seeing beyond it. But there is no actual separation— the only separation is our inability to perceive every layer of Reality in front of us. But even though we’re not able to perceive every layer of Reality-- just like we’re not able to see atoms bouncing around, or molecules doing their stuff, or perceive the growing of a tree as it happens, or whatever-- doesn’t mean the Reality doesn’t exist. Those are material examples of how our senses fail us— the same thing holds true on the spiritual level.
Look at all the encounters with angels in the Bible. How many of them happened while the person was awake? You’ve got the Annunciation and Daniel and Zacharias— but most of them are in disguise (a la Raphael in the Book of Tobit) or in dreams (Joseph, the Three Wise Men, etc). But yeah, a lot of it is an effect of us separating ourselves from God through sin. We’ll always be very, very small, and there’s nothing we can do on our own to be able to acquire that capacity on our own---- but God’s very kind, and gives us a little taste of what we’re missing on occasion, to help us strive harder in the right direction.