Who was St. Joseph's Father? The New Testament seems to give two answers

Question

Matthew 1:16 (NASB)

16 Jacob was the father of Joseph the husband of Mary, by whom Jesus was born, who is called the Messiah.

Luke 3:23 (ESV)

23 Jesus, when he began his ministry, was about thirty years of age, being the son (as was supposed) of Joseph, the son of Heli,

The problem here is that Matthew names Jacob Jesus's Grandfather and Luke names Heli. What is going one here? A mistake? A misunderstanding of Jewish genealogies?

Answer 1

The genealogy in the gospel of Matthew is definitely the genealogy of Joseph, and the genealogy in Luke's Gospel is most likely that of Mary. This coincides with the primary audiences of the two books (Mathew the Jews, and Luke the Gentiles). Mathew would want to show according to Jewish tradition that Jesus was both a Jew and a Son of David. Luke was trying to show that Jesus was the promised redeemer that would crush the serpent's head for all of Adam's children.

For more information:

Clarke's Commentary on the Bible

That St. Luke does not always speak of sons properly such, is evident from the first and last person which he names: Jesus Christ was only the supposed son of Joseph, because Joseph was the husband of his mother Mary: and Adam, who is said to be the son of God, was such only by creation. After this observation it is next necessary to consider, that, in the genealogy described by St. Luke, there are two sons improperly such: i.e. two sons-in-law, instead of two sons. As the Hebrews never permitted women to enter into their genealogical tables, whenever a family happened to end with a daughter, instead of naming her in the genealogy, they inserted her husband, as the son of him who was, in reality, but his father-in-law.

Answer 2

The books of Matthew, Mark, Luke and John can be seen to present Christ as King, Servant, Man, and God (in that order). See E.W. Bullinger's wonderful book Number in Scriptures for more on this topic (the chapter on the number seven).

As Bullinger puts it, a king must have a genealogy, and a man should have one. You'll notice that Matthew's genealogy starts with Abraham and goes down to Joseph, while Luke's genealogy proceeds up from Joseph to Adam and God. Matthews lineage describes the royal lineage through Solomon, while Luke's lineage describes the natural line through Nathan (Solomon's older brother, the third of four sons to David and Bathsheba - see I Chronicles 3:5). The first (Matthew's) is legal, the latter (Luke's) is natural.

Both lines eventually meet when Joseph, the son of Jacob (Matthew) marries Mary, the daughter of Heli (Luke). Luke 3:23 refers to Joseph as being the son of Heli out of the Jewish legal sanction and customary practice to refer to the son-in-law as son.

To summarize, Matthew's is the genealogy of Joseph, son of Jacob. Luke's is the genealogy of Mary, daughter of Heli.

Source: EW Bullinger's Number in Scriptures