Matthew 1:19

“Then Joseph her husband, etc.] To whom she had been betrothed, and who was her husband, and she his wife according to the Jewish law, (<052223>Deuteronomy 22:23,24) though not yet come together, being a just man, observant of the law of God, particularly that which respected adultery, being wholly good and chaste, like the Patriarch of the same name; a character just the reverse of that which the Jews give him, in their scandalous f50 book of the life of Jesus; where, in the most malicious manner, they represent him as an unchaste and an unrighteous person: and not willing to make her a public example, or to deliver her, i.e. to the civil magistrate, according to Munster’s Hebrew edition.…”

“Then Joseph her husband--Compare Mat 1:20, "Mary, thy wife." Betrothal was, in Jewish law, valid marriage. In giving Mary up, therefore, Joseph had to take legal steps to effect the separation. being a just man, and not willing to make her a public example--to expose her (see Deu 22:23-24) was minded to put her away privily--that is, privately by giving her the required writing of divorcement (Deu 24:1), in presence of only two or three witnesses, and without cause assigned, instead of having her before a magistrate. That some communication had passed between him and his betrothed, directly or indirectly, on the subject, after she returned from her three months' visit to Elizabeth, can…”

“Her husband - The word in the original does not imply that they were married. It means here the man to whom she was espoused. A just man - Justice consists in rendering to every man his own. Yet this is evidently not the character intended to be given here of Joseph. The meaning is that he was kind, tender, merciful; that he was so attached to Mary that he was not willing that she should be exposed to public shame. He sought, therefore, secretly to dissolve the connection, and to restore her to her friends without the punishment commonly inflicted on adultery. The word just has not unfrequently this meaning of mildness, or mercy. See 1 John 1:9; compare Cicero, De Fin. 5, 23. A public…”

“A just man - A strict observer of the law: therefore not thinking it right to keep her. Matthew 1:21”

“1:19 As a righteous man—that is, as one who obeyed the law (see Luke 1:6)—Joseph could not take Mary as his wife since she was a suspected adulteress. He could exonerate himself by publicly exposing Mary to trial and having her put to death (Deut 22:23-27; cp. Num 5:11-31), or pay a fine and break the engagement (see also Mishnah Sotah 1:1-5). Joseph mercifully decided to do the latter quietly.”

“her husband: Lev 19:20; Deu 22:23, Deu 22:24 a just: Gen 6:9; Psa 112:4, Psa 112:5; Mar 6:20; Luk 2:25; Act 10:22 a public: Gen 38:24; Lev 20:10; Deu 22:21-24; Joh 8:4, Joh 8:5 was: Deu 24:1-4; Mar 10:4 Matthew 1:20”