1) The coming of the Holy Spirit depended on Christ’s ascension to the Father’s right hand. The Old Testament foreshadows this in II Kings 2: 9, 10, using the translation of Elijah into Heaven to paint a picture for us. Elisha continued in the spirit and power of Elijah. The Church continues in the same power that was present in Christ as he “went about doing good, healing all who were oppressed by the devil (Acts 10:38).” The Church is the extension of His Incarnation, the Body of Christ, because of the coming of the Holy Spirit.
Suggested reading: John 16:7-16
2) The world is not worthy, and cannot bear the presence of the risen Christ. He spent forty days on the earth with His disciples, but left the world because His physical presence was premature for it in its fallen condition. His resurrection signals the end of sin and death, but in order for His salvation to be made available to all nations, His resurrection is the firstfruits of immortality and the world to come. The ascension of Christ, that mysterious removal of Himself from our dimension, reminds us that the world is unworthy to have in it the perfected and immortal new man, the Second Man and Last Adam. This clarifies both the world’s captivity to sin, and the sure and certain hope that Christ will complete His work.
Suggested reading: Matt. 24:14, Rev. 5: 9
3) His command is to occupy until he comes. An army occupies only after winning the major battles of a war (Luke19:13). He said that the gates of Hell shall not prevail against His Church (Matt. 16: 18). A gate is not an offensive weapon. The purpose of a gate is to be knocked down and trampled by the invading forces. The Church is the invading and conquering force, no matter how much we may feel otherwise. The mission for us is clear, namely, to be the agent of His salvation to all nations, which is why we depend on the Holy Spirit as we remain in this unworthy world.
Suggested reading: Matthew 28: 18-20