Therefore we must pay the closer attention to what we have heard, lest we drift away from it. For if the message declared by angels was valid and every transgression or disobedience received a just retribution, how shall we escape if we neglect such a great salvation? [Hebrews 2:1–3]
If the Reformed were correct in their view of election and perseverance, this passage becomes unintelligible. It would require the author of Hebrews to be uncertain of his election (which ought to be impossible on Reformed terms) or that the elect can lose their salvation (which certainly is impossible on their terms).
Not all Reformed are subject to this criticism. My last PCA minister asserted that with respect to the doctrine of election Presbyterians ought to let Scripture interpret Scripture, and he appealed to Dt. 7. In Dt. 7 Moses says that God chose Israel: they were elect. And yet an entire generation of these elect perished. But it ought to be pointed out that this view of things is not exactly the ordinary view of the Reformed.