Well then, how else can you know that the world is contingent, if not against that which is non-contingent?
Youre asking the question while at the same time begging the question. Clearly we dont have to obtain prior knowledge of thing that is unchanging and undivided in order to understand change and division. The world is understood to be contingent because no experience is demonstrably true. The universe doesnt have to exist, and might not exist, therefore you cannot use the universe to argue to true reality or the Absolute. Your argument should be: The Absolute, therefore the universe. Instead you are forced to say: The universe, therefore the Absolute. And that is because your argument begins and ends in the universe. No universe; no argument.
Might I suggest to you that the non-contingent is passive and one in which you are totally immersed, and that is the reason you are unaware of its presence, as a fish is unaware of the sea it is totally immersed in. Both you and the fish are preoccupied with focusing on what is in the contingent world, but even this preoccupation with phenomena is possible via of the passive background.
And that is all it amounts to a 'suggestion'. Its an unproven and unprovable hypothesis, an absurdity even, where the advocate, as contingent being, hopes to demonstrate experience of necessary being.