“Then Joseph her husband, being a just man, and not willing to make her a publick example, was minded to put her away privily” (Mt. 1:19).
What does true righteousness look like in practice? Joseph was confronted with what appeared to be a clear case of infidelity when he learned that his betrothed Mary was pregnant. This verse gives his response to the news: “being a just (or righteous) man and not willing to make her a publick example”. These words seem to indicate that BECAUSE Joseph was a righteous man he did not want to expose Mary’s apparent sin and cause her to be stoned as the Law required.
But there is another way of rendering this verse, which reads in Greek, “Ἰωσὴφ δὲ ὁ ἀνὴρ αὐτῆς, δίκαιος ὤν, καὶ μὴ θέλων αὐτὴν παραδειγματίσαι, ἐβουλήθη λάθρᾳ ἀπολῦσαι αὐτήν.” The key participles here are “δίκαιος ὤν (being righteous)” and “μὴ θέλων (not willing)”. These participles can be understood in more than one way and the English translation is unable to give the same variety of translations as the Greek. While most translations take the relationship between them to be causal (Joseph showed mercy BECAUSE he was righteous), some interpreters argue for a concessive translation (ALTHOUGH Joseph was righteous he showed mercy). Both Roman and Jewish law REQUIRED that marital infidelity be exposed for the purification of society from a bad member. Joseph was actually contemplating doing something unrighteous by the standards of the day in order to protect Mary.
I think this second rendering actually hints at something which St. Matthew was trying to get across in the larger context of his Gospel. Throughout the Gospel of Matthew the old (mis)understanding of righteousness according to the letter of the Law is being challenged and redefined by the words and actions of Jesus. Christ shows us that our thinking had been too limited in regards to the true nature of righteousness. In Him righteousness and mercy are no longer at odds with each other. He tells us that our righteousness is not to be the same as that of the scribes and Pharisees (Mt. 5:20), the righteousness He preaches leads us to show mercy to even the least of our brethren (Mt. 25:35-40), He reminds us of the words of the holy prophet Hosea that God prefers mercy even over the the just sacrifices God Himself had ordained (Hosea 6:6; Mt. 9:13, 12:7). He lived out this new form of righteousness by being a friend of tax collectors and sinners. He lived it out to the uttermost by His merciful sacrifice on the Cross in order to blot out the handwriting of ordinances which was against us (Col. 2:14).
Because the participles in this verse can be taken either way it is almost like a door swinging on its hinges. On the one side stands Joseph deciding to do something objectively unrighteous and hide what he believed to be a sin because of the compassion in his heart. He steps through the Door (John 10:9). He comes out on the other side and his action has been transformed. Now he is determined to protect Mary not ALTHOUGH he is righteous but BECAUSE he is righteous. This is how powerful the Incarnation is. Even though Jesus was still a foetus in the womb of Mary, His very presence in the world had already begun to change everything. Truly, in Him, “Mercy and truth are met together; righteousness and peace have kissed each other. Truth shall spring out of the earth; and righteousness shall look down from heaven (Psalm 84 :10-11).”