Hardly anyone is willing to take responsibility for his actions. Are people innocent when leaders lead them astray? Can we rightly blame others for our actions?
The same attitudes in Malachi are prevalent today. The offenses mentioned are 1) arrogance, 2) mixed marriages, and 3) neglect of tithes.
God is training us as a holy priesthood, called to offer unblemished sacrifices, honoring His name, putting down pride, presumptuousness, and arrogance.
Just because we keep God's feasts does not necessarily mean we are in sync with God's Law or intent. The Israelites kept the feasts in a carnal manner.
We must be careful when we ask for justice, for our request might come back to bite us. Those begging for justice will indeed get what they ask for.