The problem with your reasoning is that your assessment of 'Universal' has to pass through you. You are the genesis of this moral system. That you appeal to an authority (The Divine) and attribute the implantation of that code to your authority doesn't factually establish anything you believe...
I’ll give you the Readers Digest of how I came to this belief -
I grew up in a very strict conservative Christian home, from a pair of devout families. In 2001, I lost my father, the most truly good and devout person I’d ever known, just as he was about to being able to live life for himself. Lost to Cancer he probably got in Vietnam. ON HUS 54th BIRTHDAY.
This drove me away from the church and into a spiritual search that took almost theee years and pretty much every religion and philosophy you could imagine. Among those things was the book “When bad things happen to good people”.
That book opened my eyes to something... an Omnipotent God cannot also be a Good/Just one if one believes a Man can be good or Just. Then I looked back into history and mythology and realized our ancestors realized that thousands of years ago.
The more I looked the more things made sense. This life is a test of the Soul. A test to see if we will take the easy road or the hard one. With the fate of our Soul hanging in the balance and happiness/pleasure being the enemy.