Luke 1:5 reads; “In the time of Herod king of Judea there was a priest named Zechariah, who belonged to the priestly division of Abijah; his wife Elizabeth was also a descendant of Aaron.” So we see that both Zechariah and Elizabeth were of Levitical lineage, of Aaronic descent, making John the Baptist a full blooded Aaronic priest, and rightfully so. My confusion comes from Luke 1:36, “Even Elizabeth your relative is going to have a child in her old age, and she who was said to be barren is in her sixth month.” From Mary’s genealogy in Luke 3:23-38 it is apparent that she is of Judean lineage, of Davidic descent. Therefore, Jesus is rightly called the son of David. How can Elizabeth and Mary be related when they come from completely different tribes?
Being 2 of the 12 sons of Jacob (also called Israel) Elizabeth’s ancestor Levi and Mary’s ancestor Judah were brothers. The children of brothers are cousins. The Greek word translated relative in Luke 1:36 also means kinsman or cousin and in the broadest sense Mary and Elizabeth were cousins. Even though many generations of Israelites had been born since the time of Levi and Judah, the Lord saw all of the descendants of Jacob’s 12 sons as belonging to one family. In fact He refers to them as the children of Israel 591 times throughout the Bible.