The western churches celebrate Advent for 4 Sundays before Christmas. Advent means waiting. The first 2 weeks is waiting for the arrival of Jesus for the second time. The last 2 weeks looks at the arrival/ incarnation of Jesus on Christmas Day. Christmas has already happened. What is yet to happen is the second coming of Jesus which we believe will happen.

In the Nicene Creed, it states:

Jesus was crucified for us; he suffered and died and was buried (Matt 27:2, 26)

And the third day rose again according to his will
and ascended into heaven, and sat on the right hand of the father (Mark 16:19)

and shall come again in his great glory to judge both the quick and the dead (Acts 1:11)
whose kingdom shall have no end. (Luke 1:33)

The ascension scene is described in Acts 1: 9-11 as follows:

Jesus Ascends to Heaven

9 Now when He had spoken these things, while they watched, He was taken up, and a cloud received Him out of their sight. 10 And while they looked steadfastly toward heaven as He went up, behold, two men stood by them in white apparel, 11 who also said, "Men of Galilee, why do you stand gazing up into heaven? This same Jesus, who was taken up from you into heaven, will so come in like manner as you saw Him go into heaven."
NKJV

Acts 1:11 clearly states that Jesus will come again. The first time He came in to the world was shrouded in secrecy and Jesus came as a helpless baby on Christmas Day. But the second coming will be a show of strength and Jesus will come in grandeur. Jesus will come in the sky surrounded/accompanied by the angels.

But the problem is that no one knows when Jesus will come the second time; only the Father knows, no one else - not even Jesus! So, we have to be diligent and be ready to receive Him when He comes. So, the advent, "Watch time".

Interestingly, if you examine some of the ICONS of Orthodox Church depicting the ascension, it is not clear whether Jesus is going from the earth to heaven (ascension) or coming back from the heaven to the earth (second coming). The artists have left it intentionally vague. The Orthodox Church believes that we are under His reign while waiting for His return to establish His kingdom in its fullness.

Jesus has given us some signs indicating his imminent second arrival. We contemplate on those during this period between the Feast of Sleebo and the Koodosh e'to - the official start of the new Church calendar year. Between the Kudosh e'to and Christmas we will celebrate the advent season - the birth of Jesus.