Malachi 2:10-3:15

The 2nd Section of Malachi deals with the 'Sinful People'
Beyond their bringing of 2nd rate sacrifices....
They were involved in 3 key areas of unfaithfulness

1) Unfaithful in their marriages (2:10-16)
2) Unfaithful in their trust in God (2:17-3:5, 3:13-15)
3) Unfaithful in their tithes & offerings (3:6-12)

Unfaithfulness in their marriages
Though some have argued that 2:10-12 refers specifically to idolatry, I think it's just another component of the marriage issue. They had broken faith with one another in two ways. First, they had entered into marriages with pagans despite being commanded not to do so. Second, they have broken off marriages to their Jewish wives. Despite these 2 wicked acts, the people were continuing to make offerings and sacrifices to God. But it was an empty religious ritual minus obedience. God hated their divorces (and perhaps even physical abuse was involved, v. 16). He commanded them to guard their marriages against temptations.

Unfaithfulness in their trust in God
The Jews in Malachi's day were making bold statements against God's justice. They were questioning whether He was involved in His creation or not. Would He come and do right? God's reply through Malachi isn't the response they were hoping for! God was going to send a messenger (John the Baptist) before He came to the temple. But God had a question for them. Was His coming good or bad news for the Jews? In fact, His coming would be BAD news for them since they themselves were wicked. But out of that judgment certain members will come forth as gold, refined.

Unfaithfulness in their tithes & offerings
One of the ways to 'return' to right relationship with God is to address the area of giving. The Jews in Malachi's day were 'robbing' God by not bringing their tithes and offerings to the temple. This resulted in the temple staff forsaking their work in order to meet their personal needs. God promised them that if they returned to Him in faithfulness in this area, He would bless them greatly.