I don't know what the message the writer want to send. But I know what kind of message I've gotten from it.
The full name of the Śūraṅgama Sūtra includes a word 密因，which someone translate it into "Hidden Basis" or "Secret Cause".
Which thing is hidden? What is the ultimate secret?
If you've watched the movie "Matrix", you maybe understand the hypothesis of "Brain in a vat",
which tell us there could be a hidden secret truth behind everything we sense.
Let me quote some "key principle" from wikipedia as follow.
Pratītyasamutpāda  (Sanskrit: प्रतीत्यसमुत्पाद pratītyasamutpāda; Pali: पटिच्चसमुप्पाद   paṭiccasamuppāda), commonly translated as dependent origination, or   dependent arising, is a key principle in Buddhist teachings, which   states that all dharmas ("phenomena") arise in dependence upon other   dharmas: "if this exists, that exists; if this ceases to exist, that   also ceases to exist".
The Śūraṅgama Sūtra tells me this "principle" is wrong.
If  you think that that thing is depended on this thing, or the other way,  this thing is depend on that thing.If you persist that something is   depend on the other things. Forest is based on woods, castles is based   on bricks. You are wrong.
According  to the Śūraṅgama Sūtra, all your problems and anxieties and sufferings  is because you are too much clinging to the sensed "woods" or "bricks".
You  are too much believing that with all "the small Lego toy pieces" you  have you can build everything, you forget the real basis, the hidden  basis, the secret basis or cause," the toy factory". (Everything depends  on it, not each other.)
And  according to the Śūraṅgama Sūtra, what is this toy factory, is it God?  is it Śūnyatā？is it some basic particle, some basic energy, or other  objective basis? the answers to all these questions we can never know.  It is the ultimate secret, and everlasting secret.
Anyone  who thinks himself figure it out, especially because he experience some  special or unique, is enchanted and deluded by images (phenomena), and  forget or don't realize the "mirror" or "screen" "TV set" "stage", THE  UNKNOWN ULTIMATE SECRET SOURCE,
which  is always unknown. No matter how much you know from some kind of   spiritual experience or other mysterious experience, there is still THE UNKNOWN.
The  Śūraṅgama Sūtra list the special experiences people gotten from  meditation as fifty 魔， someone translate it into demon. I prefer to  translate it as obstacle such as blinders.
Don't  cheated by what you see, what you feel, what you sense, what you  experience. They can never be the ultimate truth or the ultimate true nature of   yourself. Thus no one knows the final answer. It is always hidden by   what you see, including blackness or emptiness, or nothingness (like   space). These are all blinders. We'd better admit that we don't know it,  don't pretend to a saint which actually could be called a demon   instead.

Can enlightenment be lost?

Anything that can be obtained can be lost.
If enlightenment means you can obtain something like light, you can also lose it.
Light is important, because it symbolize something can make you see.
But we can also see darkness.
With or without outer lights, we can see.
Because we are lives who all have inner lights.
The inner light is always there,
not something we gain from some special experiences which we call them enlightment,
so it can never be lost.