Psalms 78:2 - Matthew Poole's English Annotations on the Holy Bible

Open my mouth, speak to you with all freedom and plainness, in a parable; uttering divers and weighty sentences (for such are oft called parables in Scripture) or passages of great moment for your instruction and advantage. Dark sayings; so he calls the following passages, not because the words and sentences are in themselves hard to be understood, for they are generally historical and easy, but because the things contained in them, concerning God's transcendent goodness to an unworthy people, and their unparalleled ingratitude for and abuse of such eminent favours, and their stupid ignorance and insensibleness under such excellent and constant teachings of God's word and works, are indeed prodigious and hard to be believed. Of old; of things done in ancient times, and in a great measure worn out of men's minds.