"But ye shall receive power, after that the Holy Ghost is come upon you: and ye shall be witnesses unto me both in Jerusalem, and in all Judaea, and in Samaria, and unto the uttermost part of the earth" (Acts 1:8).
These very familiar words of the Lord Jesus are commonly considered as a statement of His Great Commission, commanding us to go "into all the world, and preach the gospel to every creature" (Mark 16:15). Actually, however, it is not given here as a command, but rather as a declarative statement--indeed a prophecy--saying that we shall witness for Him to the very ends of the earth.
Then, His disciples were promised that "this same Jesus" would return (Acts 1:11), with the promise clearly tied to the prophecy. Just a few weeks previously they had asked: "What shall be the sign of thy coming?" (Matthew 24:3). And Jesus had answered: "This gospel of the kingdom shall be preached in all the world for a witness unto all nations; and then shall the end come" (v.14). Mark recorded His answer very simply: "The gospel must first be published among all nations" (Mark 13:10).
Peter says that the Lord may seem to have delayed "the promise of His coming" because He "is longsuffering . . . not willing that any should perish," urging us to "account that the longsuffering of our Lord is salvation" (II Peter 3:9,15), suggesting that we should be "Looking for and hasting unto the coming of the day of God" (II Peter 3:12).
We can hardly draw any other conclusion from such passages than that, if we want the Lord to return quickly, we can hasten His coming by fulfilling His command and His prophecy, doing whatever we can to publish His gospel among all nations. His coming has always been imminent, because this could well have been done--and can be done--at any time. But it evidently has not been done yet. HMM