John Calvin Commentary Luke 1:56

"And Mary abode with her about three months, and returned unto her house." — Luke 1:56 (ASV)

The substance of this narrative is that the birth of John was distinguished by various miracles, which gave reason to expect that something great and remarkable would appear in the child himself in the future. For the Lord determined to confer upon him from the womb remarkable tokens, so that he might not afterwards come forward as an obscure and unknown person from the crowd to discharge the office of a Prophet.

First, Luke relates that Mary remained about three months with her cousin — or, in other words, until the birth of the child. For it is probable that she had no other reason for staying so long but to enjoy the display of divine grace, which the angel had made known to her for the confirmation of her faith.