How were Mary and Elizabeth related, outside of the obvious of being of the children of Abraham. Mary was of the tribe of Judah, and Elizabeth would have been a Levite. How could Mary and Elizabeth be related that would make Jesus and John to be considered cousins?
Luke 1:36
And behold, your relative Elizabeth in her old age has also conceived a son, and this is the sixth month with her who was called barren.
The declaration in Luke 1:36 that Elizabeth is a relative of Mary comes from Gabriel.
From Gabriel's introduction of himself to Zacharias we know that he is God's messenger and stands in the presence of God .
Those who believe God's Word by faith will thus find a way to understand how Elizabeth is indeed an historical figure and is both a 'daughter of Aaron' as recorded by Luke, and a 'relative' of Mary, mother of Jesus, as declared by Garbriel.
A reasonable explanation is that Elizabeth and Mary were related through Elizabeth's mother and not through her father. If Elizabeth's mother was of the Tribe of Judah but her father was of the Tribe of Levi she could be called a daughter of Aaron. Mary's father was certainly of the Tribe of Judah, and so was her husband, Joseph. Mary's mother could also have been of the Tribe of Judah.
This gives three possible ways in which Mary could be a relative of Elizabeth's, either by blood or by marriage. The term 'relative' is most likely referring to a blood relationship, so it is reasonable to believe that they were related through Elizabeth's blood relationship to either Mary's father or mother in the Tribe of Judah.
Luke 1:36 describes Mary and Elizabeth as relatives (συγγενίς). The King James Version describes them as cousins, but most other translations simply say they were relatives. Given the ambiguity of the text, we can not say that Jesus and John were actually (second) cousins, but it appears from this that they were related and would have known each other.
In ancient Jewish society, priests had to be from the tribe of Levi,but any woman of the tribe of Judah could marry a priest. This means that Elizabeth need not have been a Levite. However, there is another explanation for the relationship that is only described in Luke's Gospel, which can be deduced from the views of some New Testament scholars.
Uta Ranke-Heinemann, in Putting Away Childish Things, finds much that is problematic about Luke's depiction of Elizabeth. On page 46, she concludes that Elizabeth was not a historical person, saying this is proved by the historically more credible report in John that Jesus and John the Baptist did not know each other. John Shelby Spong agrees with Ranke-Heinemann, saying in Why Christianity Must Change or Die: A Bishop Speaks to Believers In Exile, page 35, that what makes him suspicious is that Elizabeth in Hebrew would be Elisheba - a name that appears only once in the Old Testament (Exodus 6:23), where she is the wife of Aaron, the brother of Moses. Luke 1:5 introduced Elizabeth as the daughter of Aaron, so had Aaron and Moses in mind when he wrote his gospel.
According to Jewish law, there was no inconsistency in Elizabeth being a relative of Mary, as described in Luke's Gospel. In any case, some scholars and theologians such as Ranke-Heinemann and Spong, provide a clearer resolution based on Elizabeth's supposed legendary status.
Just a thought, Mary's mother also can be from the line of Levi. Making her both from Kingly and Priestly line. Well the Lord Jesus is both King and Priest isn't it.
