‘You have put gladness in my heart,
More than those have when their corn and their wine are increased.'
The greatest gladness in life in an agricultural society was for the corn and the wine to increase. And the harvest festivals, in a good year, were their time of greatest rejoicing (see Isaiah 9:3; contrast Jeremiah 48:32-33). It meant plentiful food, much enjoyment, increasing wealth and a year of fullness. But the gladness that YHWH puts in the heart, David says, is greater far than that. David rejoiced in the pouring out of His goodness for it far exceeded the blessing of the harvest. And he especially rejoiced in that in his present situation God was working for Him and would continue to do so.
But every child of God can echo his experience. Like David they may sometimes find themselves in tight corners, seemingly unable to escape. But when His time comes they will be delivered, and great will be their rejoicing, far exceeding anything that the physical world offers.