"'They offer sacrifices given to me and they eat the meat, but the Lord is not pleased with them. Now he will remember their wickedness and punish their sins: They will return to Egypt.'" NIV translation
The people were going through their rituals and using words but did not realize that words and rituals could not save them. In fact, rituals become a trap and ultimately lead to slavery. This is a reminder for us that we are saved by the grace of God and not through anything that we have done or will do. We may be quick to judge Israel's actions here but, even in the church today, rituals and traditions can become a trap that causes men to fall from grace.
"'Israel has forgotten his Maker and built palaces; Judah has fortified many towns. But I will send fire upon their cities that will consume their fortresses.'" NIV translation
The charge against God's people is simply that they placed their trust in man's efforts instead of God's provision. Men struggle with their desire to do something to earn favor and salvation from God instead of following Him by faith. It was true during the prophet's time and it is just as true today.