And God would have fed them with the fat of wheat, and with honey out of the rock would I have sufficed thee.
Ps 81:16 (Geneva Bible)

At the end of Psalm 81, the psalmist talks about a people who have closed their ears and hearts to God. But it need not be this way. The grace of God is still grace, even when we think we can reject it. The final verse is a demonstration of this. Fat does not drip from wheat stalks (after all, מֵחֵלֶב חִטָּה doesn't mean finest wheat, but wheat-fat), and rocks to not ooze honey. Yet this is what is on offer to the people of God. We can talk all we want about what's really meant by these strangely beautiful images, but I would maintain that they are but metaphors for grace—something impossible on their own, and inexplicable in human terms, and yet something unbidden and unearned that drips and flows from the bounteous hand of God for the nourishment of the elect:
Open thy mouth wide, and I will fill it. 

Ps 81:10 (Geneva Bible)

Open my heart to receive your goodness, Lord—a goodness that is out of reach without you; in Jesus' Name, who taught me to pray...