Because you did not serve the LORD your God with joygulness and gladness of heart, because of the abundance of all things, therefore you shall serve your enemies whom the LORD will send against you, in hunger and thirst, in nakedness, and lacking everything.--Deuteronomy 28:47-48a (ESV)
In the midst of God pronouncing curses on those who transgress His law (most of Deut. 28 consists of curses for sin), He teaches us what our response to prosperity should be. Verse 47 implies that when God gives us abundant gifts, our right response is joyful and glad service to Him. Indeed, not doing this warrants the curse of verse 48.
The application of this command is simple: When God makes any good thing abound to you, serve him with joy and gladness.