A classic objection to transubstatiation, famously pressed by Wycliffe, is that according to the Catholic understanding of the doctrine, the accidents of bread and wine persist even though the substance of bread and wine no longer exists. But in Aristotelian metaphysics, accidents are essentially dependent on their substance.
Eternalism—the view that past and future and present things all exist—provides a neat way for the Catholic to respond to Wycliffe. One can, if one so wishes, hold on to the idea that it is metaphysically necessary that a subject exists if an accident exists. But one denies that it is metaphysically necessary that the subject exists at the same time as the accident. The eternalist then holds that even if the bread and wine have perished at a time t1 after transubstantation, nonetheless it is true at t1 that the bread and wine exist, where the "exist" is tenseless. On this view, every accident has a subject in the same world but not always at the same time.