Matthew wishes his Jewish audience to see — through the structure of his geneology — that Jesus is the Messiah. Beginning with Abraham (Matt. 1:2), two of the three sets of fourteen generations in the list of ancestors find conclusions in David (v. 6) and the exile (v. 11). Of course, Abraham, David, and the deportation of Israel to Assyria and Babylon (2 Kings 17:7–23) are pivotal points in the story of God’s people. David fulfilled, in shadowy form, the Abrahamic promises, but his sons lost the kingdom. Yet Yahweh pledged to send His servant, a greater son of David, to end Israel’s exile (Amos 9:11–15). The placement of Joseph’s family at the end of the third set of fourteen generations (Matt. 1:16) tells us that they will be the people God uses to restore the kingdom.
Joseph is the adopted father of the Son who fulfills ultimately all of the Lord’s promises. Righteous Joseph is a fine choice to raise the Christ, for he loves and delights in God’s law. According to the custom in Joseph’s day (circa 4 b.c.), he and his bride-to-be would be engaged for a full year (without cohabitation), and would require a legal divorce to dissolve their bond. Mary becomes pregnant during this period (v. 18), which implies the couple has had sexual relations unlawfully before the proper time. Joseph is not guilty of this sin and needs to initiate a divorce to preserve his righteousness and good name. He is unwilling, however, to put Mary to shame, and so he pursues a private divorce, an acceptable provision according to the law of Moses (Num. 5:11–31), in order to avoid embarrassing Mary publicly (Matt. 1:19).
Neither Mary nor Joseph has sinned, and an angel is sent to tell Joseph not to divorce her. Mary has become pregnant by the power of the Holy Spirit and will bear One who will “save his people from their sins” (vv. 20–21). This Jesus, John Calvin tells us, delivers His people in two moves. “Having made a complete atonement, he brings us a free pardon, which delivers us from condemnation to death, and reconciles us to God. Again, by the sanctifying influences of his Spirit, he frees us from the tyranny of Satan, that we may live ‘unto righteousness’
(1 Peter 2:24).”
In mercy, Joseph did not call for the Law’s harshest penalties on the wife he thought unfaithful (Deut. 22:13–21). Depending on the offense and its circumstances, while the church is always called to discipline, it is not always required to exact the harshest penalty. Applying God’s Word rightly involves much prayer. Matthew Henry wrote: “Were there more of deliberation in our censures and judgments, there would be more of a mercy and moderation in them.”