Forty days from the day He rose from the grave, Jesus ascended into heaven. Here is how Luke described the event:
Therefore, when they [the disciples and the risen Christ] had come together, they asked Him saying, "Lord, will You at this time restore the kingdom to Israel?"
And He said to them, "It is not for you to know times or seasons which the Father has put in His own authority. But you shall receive power when the Holy Spirit has come upon you; and you shall be witnesses to Me in Jerusalem, and in all Judea, and in Samaria, and to the end of the earth.
"Now when he had spoken these things, while they watched, He was taken up and a cloud received Him out of their sight..." (Acts 1: 4-9, New King James Version).
Because the date of Easter varies from year to year, the celebration of the Ascension moves with it. It always falls on the fortieth day from Easter and, since Easter always falls on a Sunday, Ascension Day always falls on a Thursday; it is frequently called "Holy Thursday."
Ascension Day celebrates Christ's exaltation. While on earth, He was a servant. Now in heaven, He is the ruler and Lord of all. By entering heaven as the representative of mankind, He completed the work of our salvation and guarantees the eventual glorification of all who love Him.
Just as Jesus went up in the clouds, He will return the same way. Again Luke described the scene:
"And while they looked steadfastly toward heaven as He went up, behold two men stood by them in white apparel, 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.'"
This is the great hope of all Christians. For just as Jesus went into heaven, so will all Christians. Those who are dead will rise first; those who are living will be caught up to meet Him in the air, according to Paul, writing to the church at Thessalonica. With this hope in mind, Christians sometimes conclude their meetings with the words, "Come Lord Jesus."
Adapted from ChristianHistoryTimeline.com.