Atos 1:9

Jesus Christ’s ascension necessarily preceded the descent of the Holy Spirit to baptize and indwell believers, in God’s plan (John 14:16; John 14:26; John 15:26; John 16:7; Acts 2:33-36). "While they were looking on" stresses the fact that the apostles really saw Jesus ascending, which they bore witness to later. This reference supports the credibility of their witness. In previous post-resurrection appearances Jesus had vanished from the disciples’ sight instantly (Luke 24:31), but now He gradually departed from them. The cloud seems clearly to be a reference to the shekinah, the visible symbol of the glorious presence of God (cf. Exodus 40:34; Matthew 17:5; Mark 1:11; Mark 9:7). [Note: See Richard D. Patterson, "The Imagery of Clouds in the Scriptures," Bibliotheca Sacra 165:657 (January-March 2008):18.] Thus what the disciples saw was the symbol of God’s presence receiving and enveloping Jesus into heaven. This connoted God’s approval of Jesus and Jesus’ entrance into the glorious presence of God.

"It was necessary that as Jesus in a moment of time had arrived in the world in a moment of time He should leave it." [Note: Barclay, p. 6.]