Luke 1:36

And behold thy cousin Elisabeth,.... For though Elisabeth was of the daughters of Aaron, or of the tribe of Levi by her father's side, yet might be of the tribe of Judah by her mother's side, and so akin to Mary. The Persic version calls her "aunt by the mother's side": intermarriages between the two tribes of Levi and Judah were frequent; nor were they at all contrary to the intention of that law, that forbid the tribes to intermarry, which was to preserve the inheritance in each tribe, since the tribe of Levi had none at all. Though she might be called her cousin in a more general sense; it being usual with the Jews to call all of their own nation their kinsmen and kinswomen, according to the flesh: but the former sense seems more agreeable; and so Mary is directed to her own family, and to her own relations, and known friends, for a sign, by which her faith might be confirmed, in what the angel had said unto her; for if she found the one to be true, she might conclude the other was also; which is as follows:

she hath also conceived a son in her old age: though Mary asked no sign, yet one is given her, whereby she might know the truth of what was spoken: for if it should appear that Elisabeth had received strength to conceive, as was declared by the angel; and that a son, too, which he could not have known without a divine revelation; and that in her old age, which, was extraordinary and supernatural, she might assure herself, that the message brought to her was from God; and that she likewise, though a virgin, might conceive, and bear a son: the angel adds, as a further testimony of the truth of things;

and this is the sixth month with her who was called barren. Elisabeth, was generally known to be barren, and was, by way of reproach, usually called so, but was now six months gone with child; so that it was a plain case, and out of question; the signs of her pregnancy were very apparent.