A parable and a dark saying is like a riddle: a riddle is a saying of something you can’t figure out unless you are given the simple key. The history of God’s people is recounted from the Exodus to the reign of David as king.
The riddle is why did the people act so faithless, unbelieving, rebellious and idolatrous in the obvious face of all the wonderful miracles of salvation and provision of God’s grace? But even more: the riddle is also about why did the Lord act so faithfully, wonderfully and mercifully to His faithless people?
It was irrational for the people who were miraculously delivered and provided for to respond in Unbelief and rebellion. It doesn’t make sense. The Sin of Unbelief may still be the greatest Enemy with which we have to deal. But it was irrational for God to continue faithful to His promise and covenant in the face of their unbelief. It doesn’t make sense. The wrath of God makes sense; the faithfulness does not.
The answer to the riddle: Grace! The human mind will never, even in eternity, plumb the depths of the mystery of the Grace and Love of God.