Adam Clarke on Matthew 1:19

To make her a public example - Παραδειγματισαι, to expose her to public infamy; from παρα, near, and δεικνυμαι, I show, or expose; what is oddly, though emphatically, called in England, showing up - exposing a character to public view. Though Joseph was a righteous man, δικαιος, and knew that the law required that such persons as he supposed his wife to be should be put to death, yet, as righteousness is ever directed by mercy, he determined to put her away or divorce her privately, i.e. without assigning any cause, that her life might be saved; and, as the offense was against himself, he had a right to pass it by if he chose. Some have supposed that the term δικαιος should be translated merciful, and it certainly often has this signification; but here it is not necessary.