It is a Jewish name (Yohanan) and it means "God is gracious".
Why Elizabeth have her son that name and why Zechariah confirmed it was not mentioned.
But we can suppose, and quite correctly, that she was expressing her thanks and praise to God for this gift of grace in her son, and that God was merciful to her and saved her from the shame of being barren.
Indeed the name "John" was very befitting for the Baptizer because he was the herald of a more important person.
He ushered in the appointed time of grace.
In fact he ushered in the fullness of grace that was embodied in the person of Jesus Christ.
In Jesus Christ, God came as a man to visit His people and to redeem them from the slavery of sin.
As it was then, so it is now still. Every moment is a time of grace.
God still visits us not only to save us but to make us the light of the nations, so that salvation may reach all nations, as we heard in the 1st reading.
May we live each moment in grace of God, so that we may be instruments of light and life to others.