In this verse God was confronting the nation of Judah. For they had been practicing religious festivals of their own design in direct rebellion against Him. In other words, they were taking God’s Word – adding and twisting it to fit their own desires and notions. Kinda sounds like religion today where God’s Word has been spun and misinterpreted to become more politically correct and not offensive anyone. But man’s job is not to reinterpret God’s Word in order to make everyone feel better. Man’s job simply is to obey what God has already written.