The Hebrew text of this portion of Malachi is difficult. NIV has made a plausible and understandable translation. Even though the text is problematic, this section remains the most outspoken condemnation of divorce to be found in the OT. It comes at the point in the prophet's argument where he turns from his castigation of the priests to condemn the people for their wickedness. He does so in the context of dealing with the question raised by the people as to why Yahweh pays no attention to their acts of worship (vv. 13-14).
Some would see in the question Have we not all one Father? Did not one God create us? (v. 10) an explicit affirmation of the oneness of humankind. But the context clearly limits the statement to the Jewish people. They are inextricably bound together by the covenant God established with their ancestors, a covenant they habitually violate. Not only have they been derelict in the way they have slighted the services of the temple, but now the prophet points out that which is even more vile. They have desecrated the sanctuary where God has placed His name by marrying the daughter of a foreign god (v. 11). Thereby they have profaned that which was holy.
In 2:13ff. the prophet likens the Jews' unfaithfulness to their spouses and the breakup of their marriages to the nation's forsaking God, their husband (see Hosea).