How do we know John the Baptist's birth was God's promise?

In Luke 1, the angel Gabriel appears to Zacharias to announce that his wife, Elizabeth, will bear a son named John. This event confirms the long-standing promise of God to send a messenger to prepare the way for the Messiah. The prophecies from Malachi 3:1 and 4:5-6 indicate that God would send Elijah before the great day of the Lord, which is fulfilled in John the Baptist's role. This narrative serves to illustrate God's faithfulness in fulfilling His promises, demonstrating His sovereignty over the unfolding of salvation history.