At the macro level, the title of the poem sets a reader to wonder: What sort of changes? Why "changes"? What is change? What's the end, the result, or outcome of mere change? The alleged topic of Ovid's poem seems to be more of the nature of a verb than of a noun. Some person, place or thing undergoes change, and becomes some other person, place or thing. The interest, the game, the poetry is usually in the act of changing -- the sudden arrest or surprise:
While she was still speaking, the soil covered her shins; roots, breaking from her toes, spread sideways, supporting a tall trunk; her bones strengthened, and in the midst of the remaining marrow, the blood became sap; her arms became long branches; her fingers, twigs; her skin, solid bark. And now the growing tree had drawn together over her ponderous belly, buried her breasts, and was beginning to encase her neck: she could not bear the wait, and she sank down against the wood, to meet it, and plunged her face into the bark. (Myrrha)
These changes can seem trivial -- a too-clever serving maid becomes a weasel. But some are more epochal: Occurrences that change the face of nature and of nations -- the flood, for example. Or expansions of the range of human potential -- Heracles. Or, a meditation on the ephemerality of what we take to be the Real, a questioning of whether there is any abiding Being behind the seemingly incessant world of appearances.
The broadest sense of "metamorphoses" -- that everything passes, including heroes, nations, lawgivers and artists -- can threaten entities that carry a huge ideological investment in the presumption of their stability and immortality, such as the Roman empire. For a writer of epic like Virgil, the song of Aeneas depicted the working out in history of a providential intention that arose outside of history, in the deathless intent of gods, or Fates. The understanding that nothing is set in stone -- not even Rome -- would challenge those beliefs and the pieties that they bring in tow.
A few broad strokes to flesh this out a bit: From early on, Ovid paints a world that seems inclined to seek order -- it's made of elements that sort themselves into higher and lower, hotter and cooler, etc. -- but that inclination is imperiled by the nature and existence of amor. Nothing, Book 1 makes clear, not even Apollo or Zeus, is stronger than love, and the gods whose purview includes serious matters are often away, missing, caught in domestic farces or low comedy, leading to serious consequences for those they love, or those who depend on their attentiveness for good outcomes to occur.
A world given over to lapses of attention, gaps in oversight, is a world in which error can gain the upper hand; things can go astray. When Hera seduces Zeus in the Iliad, the Trojans nearly vanquish the Greeks. Is it even possible to imagine Yahweh of the Old Testament having a dalliance with the Queen of Sheba? The Biblical world is one in which a supreme Being stays on top of every last detail, and to err is pretty much strictly human. The multi-valenced world of the Greeks is rife with competing forces. Like the market, no single actor has perfect intelligence of all that goes on -- unless it's the Fates. Yet as Themis noted in Book 9 of Ovid's poem, there are occasions when fate itself can be revised, when necessary.
Humanity in the Tanakh is always on its way to some future stability, to inheriting some shining city that their trusted God will lead them to, because there's a covenant, a promise, made by and to a single changeless Being in contrast with whose timelessness all human history is an instant. Humanity might fail, or fall, but that's not an indictment of Yahweh, or a fact about the way things are. The way things are hinges upon choice. Humanity changes, falls, rises, grows, sins, repents, and wavers, but it -- we -- have a contract that is firm with a partner whose order of being makes our notions of "firm" look weak and feckless. Faith in Yahweh is predicated upon historical experience -- the series of events that led to the transaction of that covenant. History is the ground of faith, and that history is found in a book, a writing.
Ovid is writing a book in which even the gods go astray, over and over, because they are tumbled by a force that deranges them and makes them rudderless, powerless. The results of those amours folles lead to extraordinary figures -- Perseus, Heracles, Medea, Minos, Pasiphae, Aeacus, Helen, Theseus, Orpheus, Dionysus, and the like -- who in turn are overturned by amor. The record of these inconstancies, these discombobulations, issues in a world constantly disarticulating, and thus lacking in continuity. A fecund world of jovial tales, issuing in more jovial tales, ad infinitum, a world without history.
Or is it that simple? When the gods do put their minds to things, there seems to be at least the shadow of consequence. Prometheus steals fire for mankind, and mankind is never the same. The Olympians rejuvenate Iolaus and the children of Heracles are saved. These might seem incremental advances in the vast nature of things, yet they seem to be telling moments, and Ovid's book tasks itself with fixing them for all time by binding them in words. Not just tales, then, but a book that ruminates upon tales. Tells what they tell.
Paradoxically Ovid's poetry works its own metamorphosis: the world gains a new immortal being, the vatic poem that sang of amor and of the new:
I will be spoken on people’s lips: and, famous through all the ages,The first word of the poem is nova, the last is vivam. The song of things forever becoming new becomes a thing that lives forever.
if there is truth in poet’s prophecies, vivam -- I shall live.
Steeped in Ovid, Dante will echo, reverse and break the cyclic world of the Metamorphoses with the title of his first book: Vita nova.