Advent has a dual purpose. The obvious part is remembering how the prophets, and the Jews, looked forward and anticipated the coming of the Messiah. And Jesus was the one they were anticipating. The other part is recognizing that as Christians we now anticipate the second coming of Jesus.
Jesus rose from the dead three days after his death, and ascended to heaven shortly after that. But he promised to return at the end of time. At that point he will be coming to bring world history to conclusion and bring his people into their inheritance.
“Then will appear in heaven the sign of the Son of Man, and then all the tribes of the earth will mourn, and they will see the Son of Man coming on the clouds of heaven with power and great glory. And he will send out his angels with a loud trumpet call, and they will gather his elect from the four winds, from one end of heaven to the other.” (Mathew 24:30-31)
That day has been delayed only because of God’s patience, to allow people more time for repentance and faith, and for the gospel to spread through the world (2 Peter 3:8-10).
But as Jesus said, “concerning that day and hour no one knows, not even the angels of heaven, nor the Son, but the Father only.” (Matthew 24:36)
So advent is a good time to remind ourselves of Jesus’ instruction: “you also must be ready, for the Son of Man is coming at an hour you do not expect.” (v44)