John Gill Commentary Deuteronomy 28:47

"Because thou servedst not Jehovah thy God with joyfulness, and with gladness of heart, by reason of the abundance of all things;" — Deuteronomy 28:47 (ASV)

Because you served not the Lord your God
By attending his worship, and keeping his commandments:

with joyfulness and gladness of heart, for the abundance of all
[things] ;
which they enjoyed in the land of Canaan, a land that abounded with all good things; which laid them under great obligations to serve the Lord: and yet, as they were wanting in a ready attendance on his worship, and in a cheerful obedience to his laws, so in their sacrifices, of praise and thanksgivings for their manifold mercies; and, because of all this, the curses written in this book came upon them.