In verse 10 Malachi does something new: he says we. Until now the LORD has spoken and the prophet has passed his words on to you. Here the prophet stands in the crowd. The first two questions have obvious answers, and the answers are the argument. One Father and one Creator mean that everyone in the room shares a source. Then the accusation arrives on a single word: faithless.
The one Father is a callback. In chapter 1 God asked where his honor was, as Israel's father (Malachi 1:6). Fatherhood first appeared as a claim on Israel's worship. Now it becomes the ground of how Israelites treat one another. If everyone comes from the same Father, dealing treacherously with a brother is treachery inside the family.
The Hebrew behind faithless means to act treacherously, to betray a trust. In the English text it appears five times from verse 10 to verse 16, in the middle of this single argument. Every sin in the section is a breach between people who were supposed to be bound: brother and brother, husband and wife. The vertical and the horizontal cannot be pulled apart. The covenant with God is kept or broken in how the covenant people treat one another.
The specific charge comes in verse 11: 11"Judah has profaned the sanctuary of the LORD, which he loves, and has married the daughter of a foreign god." The words which he loves reach back to the first words of the book, I have loved you (Malachi 1:2). Ezra and Nehemiah tell the story behind it. After the return, men of Judah married women from the surrounding peoples (Ezra 9:1-2; Nehemiah 13:23-27), and Malachi goes on to say that some were putting away the wives of their youth (Malachi 2:14-16). The dividing line was the god.
Ruth was a Moabite who entered Israel by committing herself to her mother-in-law's people and God (Ruth 1:16), and her book ends in the line of David (Ruth 4:17-22). To marry the daughter of a foreign god was to bring a second allegiance to the head of the home, and the home is where a child learns whom to worship. Deuteronomy had warned that such a spouse would turn sons away to serve other gods (Deuteronomy 7:4). The man in verse 12 still comes to the temple with his offering. That is what profanes the sanctuary: worship laid on top of a life committed elsewhere.
Paul takes the family of the one Father and stretches it. There is one body and one Spirit, one God and Father of all (Ephesians 4:4-6). Gentiles who were strangers to the covenants of promise are brought near, because Christ has broken down the dividing wall of hostility (Ephesians 2:12-14) and made them members of God's household (Ephesians 2:19). Malachi asked why we would be faithless to one another. Paul says who kept faith when we were faithless: if we are faithless, he remains faithful (2 Timothy 2:13).
Faithfulness among people is where we find out whether our worship is real. A promise to a friend, a vow at a wedding, a confidence kept: each is a place where we honor the one Father or do not. Jesus said to leave your gift before the altar and first be reconciled to your brother (Matthew 5:23-24). Whose trust have you broken that you have not yet tried to mend?
Prayer
Father, we call you our Father and then treat one another as strangers. Forgive us for the promises we have let go slack, the trust we have spent, and the offerings we have brought while a wrong sat unmended. Thank you that when we were faithless you remained faithful, and that in Christ you have made strangers into one household. Show us whom we have betrayed, and give us the courage to go first. In Jesus' name, amen.