There is a fairly addictive idea, which we get from reading Matthew 24:14. Matthew 24 is all the signs of the end. There's a long litany that are called "birth pangs," so many have concluded that (like birth pains), the more intense and the more frequent the signs, the closer we are to the end of days.
Verse 14 says, "And this Gospel of the Kingdom shall be preached in all the world as a witness to all the nations, and then the end shall come."
And from that we get the idea "finishing the task" of the Great Commission will also "bring Jesus back." It seems to me (and to many others) that this can lead to greatly impassioned mobilization calls, but it is a very bad idea, as it is very poor theology.
First, it implies that by linking the two things together ("the task is done" and "Jesus will appear") we can know when Jesus is coming. But this is something Jesus said specifically we could not know ('no man knows the day or the hour, not even the Son of Man'). Some get around this by suggesting we might not know the precise hour, but we could know the general time. 2,000 years of trying to predict the day and the hour, even generally, have proven our utter failure to do so. Sure, one day, someone will "guess right," but that will be pure coincidence.
Second, it could go so far as to imply we "control Jesus." We determine, not God, when Jesus will come back. Very, very bad theology.
Third, it could imply that we could keep Jesus from returning. Yes, I know, you think no one would want to do that. But I suggest the theoretical possibility alone is enough to disprove the interpretation.
As Lewis so quotably said, and as I am fond of quoting: He is not a tame lion. Clearly, the verse links the two things. In this sense, it is both prophecy and promise (and many disagree about the specific interpretation of the verse). But while it can be hopeful inspiration to us, it should never be taken to be some kind of control over history.
We don't work to finish the Great Commission in order to bring Jesus back. We don't have any power over that.
We work to finish the task because he gave it to us, and because we love him, we want to obey him. That's it. That's all.