You basically said that by using the word "truth", Buddha was referencing God. It's a argument based on your own theory.
I am happy to have that as my own theory, and it has some very strong basis.
As like in the Christian Bible it tells that:
"And ye shall
know the truth, and
the truth shall make you free." John 8:32
"God is a Spirit: and they that worship him must worship him in spirit and
in truth." John 4:24
"Jesus saith unto him, I am the way,
the truth, and the life: no man cometh unto the Father, but by me."
Thereby the
4 Noble Truths are an expression of the same thing =
TRUTH.
So your idea of substance is to hijack a non-religious argument and put "God did it" in front of it. Nice.
The "Big-Bang" is NOT a non-religious argument (as you call it) because explaining and understanding the Big-Bang / Creation Day is now a discussion about reality.
Atheist want to exclude God in that, but it is hard to exclude the blatantly obvious.
So where are you getting the scripture that you cite as your evidence for substance?
In this particular case then I view the 4 Noble Truths given by the Buddha are scriptures, and thereby as being scriptural evidence of substance.
When I say God then I do not mean the Christian only God but the God of everyone and of everything.
Which ultimately means that you are accountable to yourself. God is not required, unless you're saying that God immediately starts playing minute games with you the moment you sow.
I do not see it as God playing games but still yes we reap or start to reap immediately whatever we sow.
As example: When one tells a lie then they immediately become a liar, and that effect last a long time unless and or until the person properly repents including the making of amends. The same in murdering then one becomes a murderer instantly and it really does hurt and it is a type of instantaneous curse.
And it is not all negative.
As in when one does a TRUTH then the person becomes a better person, and when we do charity or compassion or express love then we instantaneously reap what we sow.
It is not really that God is looking over our shoulders but that the process is built into the system as it is a part of life and of living, which we thereby called as a TRUTH.
Or maybe the Noble Truths apply to Buddha's personal experiences -- that they are his truths -- and are not a reference to the divine.
You can put those kind of limits onto the truth(s) but I find it is as just a limitation onto your self and it only limits your self, while I reject that limitation.
The Buddha did base his truths on his own experiences, and based on his own research and his studying, but I believe that the Buddha was inspired, or more certainly his Noble Truths were inspired or inspiration.
If you want to say or believe that it did not come from God (or divine) then that is your loss and not mine.
What you view as truth is really just an opinion. It is based on your experience with the whatever scripture you follow. It is a religious opinion, and is of no more value than an atheistic opinion.
Hiding behind religious dogma doesn't make your opinion any more valid or less self-righteous.
I do not see mine as opinion or as belief because I have tested mine and put it into practice and I find mine to be true and known.
The reality of God is a thing that I know about and it is not a belief or opinion of mine.
You call that as belief or opinion and you are mistaken.
The same with the 4 Noble Truths in that I know that they are real and effective and empowering and it is not my belief or opinion as I know it to be real.
My opinion is that science is a method of understanding natural phenomena and is diametrically opposed to supernatural supposition.
It depends on how one defines supernatural - and I am not picking on words.
As like the Big-Bang is a scientific proof of God, and the Big-Bang is really a huge miracle, and science declares that the Big-Bang is not supernatural, and that means the Creation Day is not supernatural.
Our own simple solar system with the earth spinning at high speed being held perfectly by invisible powers / invisible forces which happens to be a far bigger miracle than is anything told in the Bible or in any other scriptures, and yet this too is not supernatural.
Having abundant life on earth is extraordinary and yet it is not supernatural.
As such the belief that God is supernatural is just not sound and not accurate.