Abstractions don’t exist, if by existence you mean having a certain weight or color. Neither do propositions, if by existence you mean material embodiment. And of course, by such criteria, God the Father doesn’t exist either.
But of course, abstractions still function just fine, provided the people using them are grounded in an incarnational and Trinitarian life of faith and obedience. And when people are not living that way, abstractions are death, not only of the abstracting one, but also of many millions of others (caught in the maw of modernity). Liberty, equality, and fraternity, as non-existent abstractions, have still slain their tens of thousands. Of course, on the other hand, abstractions have done a lot of good. Love, for example, is kind, and gentle. But not to anyone in particular; to be kind to someone in particular would have gotten love, the abstract noun, chucked out of 1 Corinthians 13.
So abstractions are necessary to good, healthy, concrete life in the world as God gave it to us. “Mowing the lawn is best when followed by a cold beer” is an abstraction just like “beauty without truth is as limp as truth without beauty is ugly.”
“Abstractions are bad” is a sentence which entirely depends for its sense on a robust and very healthy abstraction. So obviously, when we lament the bad effects of abstractions in philosophy and theology (and there are many such bad effects), we are actually talking about abstractions when used in a certain way, or abstractions that are given ontological zip code status up in Platoville. But abstractions when used rightly, on the other hand, are a blessing of the first rank. An honest answer is like a kiss on the lips, says Proverbs, but since this is an abstraction, nothing actually lands on the lips. And it is not even a shame.