Matthäus 1:19

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 hardly be doubted. Nor does the purpose to divorce her necessarily imply disbelief, on Joseph's part, of the explanation given him. Even supposing him to have yielded to it some reverential assent--and the Evangelist seems to convey as much, by ascribing the proposal to screen her to the justice of his character--he might think it altogether unsuitable and incongruous in such circumstances to follow out the marriage.

This evangelist begins with the account of Christ's parentage and birth, the ancestors from whom he descended, and the manner of his entry into the world, to make it appear that he was indeed the Messiah promised, for it was foretold that he should be the son of David, and should be born of a virgin; and that he was so is here plainly shown; for here is, I. His pedigree from Abraham in forty-two generations, three fourteens (v. 1-17). II. An account of the circumstances of his birth, so far as was requisite to show that he was born of a virgin (Mat 1:18-25). Thus methodically is the life of our blessed Saviour written, as lives should be written, for the clearer proposing of the example of them.

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.