Some think that this is a reference to Jesus' birth. Were there stories that were circulated among the people at that time that Jesus was not Joseph's son. They assume that he was illegitimate. It is not clear whether the story of His miraculous birth was publicly known.
Most of the commentators think that this is a reference to genealogical purity. We were not born through Hagar or the line of the Samaritans. We are from the line of Abraham. Our line is pure.,/p>