Charles H. Spurgeon on Psalms 78:2

I will open my mouth in a parable. Analogies are not only to be imagined, but are intended by God to be traced between the story of Israel and the lives of believers. Israel was ordained to be a type; the tribes and their marchings are living allegories traced by the hand of an all wise providence. Unspiritual persons may sneer about fancies and mysticisms, but Paul spake well when he said "which things are an allegory, "and Asaph in the present case spake to the point when he called his narrative "a parable." That such was his meaning is clear from the quotation, "All these things spake Jesus unto the multitude in parables; and without a parable spake he not unto them: that it might be fulfilled which was spoken by the prophet, saying, I will open my mouth in parables; I will utter things which have been kept secret from the foundation of the world." Mt 13:34-35. I will utter dark sayings of old; —enigmas of antiquity, riddles of yore. The mind of the poet prophet was so full of ancient lore that he poured it forth in a copious stream of song, while beneath the gushing flood lay pearls and gems of spiritual truth, capable of enriching those who could dive into the depths and bring them up. The letter of this song is precious, but the inner sense is beyond all price. Whereas the first verse called for attention, the second justifies the demand by hinting that the outer sense conceals an inner and hidden meaning, which only the thoughtful will be able to perceive.