“And Jesus himself began to be about thirty years of age, being (as was supposed) the son of Joseph, which was the son of Heli,”
King James Version (KJV)
3:23 And Jesus was - John's beginning was computed by the years of princes: our Saviour's by the years of his own life, as a more august era. About thirty years of age - He did not now enter upon his thirtieth year (as the common translation would induce one to think) but he now entered on his public ministry: being of such an age as the Mosaic law required. Our great Master attained not, as it seems, to the conclusion of his thirty - fourth year. Yet what glorious achievements did he accomplish within those narrow limits of time! Happy that servant, who, with any proportionable zeal, despatches the great business of life; and so much the more happy, if his sun go down at noon. For the space that is taken from the labours of time, shall be added to the rewards of eternity. The son of Heli - That is, the son - in - law: for Heli was the father of Mary. So St. Matthew writes the genealogy of Joseph, descended from David by Solomon; St. Luke that of Mary, descended from David by Nathan. In the genealogy of Joseph (recited by St. Matthew) that of Mary is implied, the Jews being accustomed to marry into their own families.
Lu 3:23-38 The Genealogy. For a comparison of the genealogies given by Matthew and Luke, see notes on Mt 1:1-17. In these notes I have followed Godet, Van Oosterzee, and others in the view that Luke gives the line of Mary, and therefore the line of Christ. Jesus was only "supposed to be the son of Joseph", but was "the son" (i.e, descendant, grandson) "of Heli", the father of Mary.