When the time arrived for Elizabeth to have her child she gave birth to a son.In insisting that he be named "John," Elizabeth was following the directive of the angel Gabriel, who had appeared to Zechariah (Lk 1:13). Why? Why this insistence on his name being John? What does it matter if he was John the Baptist or Zechariah the Baptist?
Her neighbors and relatives heard that the Lord had shown his great mercy toward her, and they rejoiced with her. When they came on the eighth day to circumcise the child, they were going to call him Zechariah after his father, but his mother said in reply, "No. He will be called John."
But they answered her, "There is no one among your relatives who has this name."
So they made signs, asking his father what he wished him to be called. He asked for a tablet and wrote, "John is his name," and all were amazed. (Lk 1:57-63)
In biblical interpretation, one generally should understand that whatever is recorded in the Bible is likely included for a reason. Likewise, it is reasonable to conclude that the Lord, through Gabriel and Elizabeth, had a good reason for insisting that he be named "John" and not something else. It is not an irrelevant or superfluous point. There is meaning to be found here.
So, what is that meaning? What are we to learn here?
Remember, in the biblical tradition, names have particular meaning, they are more than arbitrary, nice-sounding labels. Rather, the name itself signifies the person; the name is the person. So, for example, the Name of God is not merely something to call Him other than "God," His Name YHWH tells us Who and What He is -- I am. The name "Jesus," which in Hebrew is Joshua or Yeshua, tells us who He is -- God saves.
There was good reason for the Baptist to be named as he was. His name "John," in Hebrew Yôḥanan, tells us who he is -- graced by YHWH. And so he was, from the moment he "leapt for joy" in his mother's womb, being filled with the Holy Spirit, upon the visitation of Jesus, also in His mother's womb. John is the forerunner to the New Covenant, the covenant of the Holy Spirit, of God filling all the faithful with His grace to make us holy too, a sanctification that begins with Baptism and leads us to Jesus the Christ.