Malachi 2:10

Corrupt practices are the genuine fruit and product of corrupt principles; and the badness of men's hearts and lives is owing to some loose atheistical notions which they have got and which they govern themselves by. Now, in these verses, we have an instance of this; we here find men dealing falsely with one another, and it is because they think falsely of their God. Observe, I. How corrupt their practices were. In general, they dealt treacherously every man against his brother, Mal 2:10. It cannot be expected that he who is false to his God should be true to his friend. They had dealt treacherously with God in his tithes and offerings, and had defrauded him, and thus conscience was debauched, its bonds and cords were broken, a door was opened to all manner of injustice and dishonesty, and the bonds of relation and natural affection are broken through likewise and no difficulty made of it. Some think that the treacherous dealings here reproved are the same with those instances of oppression and extortion which we find complained of to Nehemiah about this time, Neh 5:3-7. Therein they forgot the God of their fathers, and the covenant of their fathers, and rendered their offerings unacceptable, Isa 1:11. But it seems rather to refer to what was amiss in their marriages, which was likewise complained of, Neh 13:23.

— Matthew Henry's Concise Commentary (public domain)

Reproof of those who contracted marriages with foreigners and repudiated their Jewish wives. Have we not all one father?--Why, seeing we all have one common origin, "do we deal treacherously against one another" ("His brother" being a general expression implying that all are "brethren" and sisters as children of the same Father above, Th1 4:3-6 and so including the wives so injured)? namely, by putting away our Jewish wives, and taking foreign women to wife (compare Mal 2:14 and Mal 2:11; Ezr 9:1-9), and so violating "the covenant" made by Jehovah with "our fathers," by which it was ordained that we should be a people separated from the other peoples of the world (Exo 19:5; Lev 20:24, Lev 20:26; Deu 7:3). To intermarry with the heathen would defeat this purpose of Jehovah, who was the common Father of the Israelites in a peculiar sense in which He was not Father of the heathen. The "one Father" is Jehovah (Job 31:15; Co1 8:6; Eph 4:6). "Created us": not merely physical creation, but "created us" to be His peculiar and chosen people (Psa 102:18; Isa 43:1; Isa 45:8; Isa 60:21; Eph 2:10), [CALVIN]. How marked the contrast between the honor here done to the female sex, and the degradation to which Oriental women are generally subjected!

— Jamieson-Fausset-Brown Commentary (public domain)