You can be sure because Christmas has always come at the same time for many years. But even before the first Christmas, people were sure that Christmas was coming. How did they know about God’s promise to send Jesus? God spoke through people called prophets to tell about His plan long before it happened (2 Peter 1:20-21).
Why did God speak through prophets? God wanted people to know about His plan and His power. Through the prophet Isaiah people learned that Jesus is powerful and the King of all the earth. Jesus is the Prince of Peace. When Jesus is King there will be peace. Other kingdoms come and go, but Jesus’ kingdom lasts forever. God wanted people to know that Jesus is God. Jesus is called “Mighty God, and Everlasting Father” because He is God. Jesus is God who came to live on earth.
What else do we learn about God through the prophets? We learn that God knows everything. God knows how many trillions of stars are in the sky and He knows them each by name (Ps. 147:4). God knows each person by name. He knows you because He created you. God knows you so well that He knows how many hairs are on your head (Matt. 10:30). God also knows what will happen in the future. God does not have to guess what will happen. He knows what will happen because He is the One who planned it. God planned the future and He has the power to make sure it will happen just the way He planned. Isaiah says, “The zeal of the Lord Almighty will accomplish it.” God has the “zeal” or power to keep His promises and do what He has planned.
– Barbara Reaoch, ‘Why Christmas?‘