I wrote this in October 2009. It bears repeating. :)
Paul writing to the Romans here assuring them of the fact of it happening but reminding them that it will not happen until a certain "number" has come in. And after that, Israel's spiritual blindness will be lifted. The NIV translation states, "full number." The full number refers to a nautical term, that a ship cannot sail until the required number of sailors had been signed on. And 'come in', well, who has not heard of the old saying, "My ship has come in"?
In 1806 the British Parliament passed an act releasing ships from having to stay in port until the 'full number' has been reached, and allowing them to sail to certain ports with less than their ship's required complement. In Dixon Kemp's "Manual of Yacht and Boat Sailing and Architecture" (11th and final edition, 1913) the "full number is defined as "Complement.-- The full number; the whole ship's crew." These two examples really have nothing directly related to the scripture in Romans, except to present original documents that show the term is indeed nautical and number-driven.
In Mark 13:32, Jesus told the Apostles, "But of that day or hour no one knows, not even the angels in heaven, nor the Son, but the Father alone." Many Christians take this to mean that since we cannot know the day nor the hour, we should not study end time prophecies. Others say that they are simply unknowable. But these notions are incorrect. Kelley again explains, using scripture, that the 'day nor hour' refers to the very end, the Second Coming of Jesus after the tribulation. As for the Rapture, we are actually commanded to watch, to look, and to encourage each other as we wait. The Crown of Righteousness is reserved for those Christians who have actively longed for His appearing.
In reality, there are several things Christians can do to hasten His coming, in reaching that pre-determined number. One is to witness, and the other is to pray. If we have shared the Gospel with an unbeliever, we should pray for that person to receive it on a prepared heart and through the drawing of the Holy Spirit. The fullness of the Gentiles will come in when that last person claims the gift of grace, so witnessing and prayer are key in that process. If we never share the Good News then obviously it will take longer to reach the "fullness." (Though God already knows when that will be.)
Since there is not a date on which God has said the Rapture will take place, praying for it to occur will not violate His precepts and it even confirms them. When we pray we are being obedient to Him who wants to hear from us. In Luke 18:1-7, Jesus told a parable about how important it is to persevere in prayer. (The Widow and the Judge). So pray for hearts to receive His Gospel and for Him to gather his sheep from the coming storm!
We are commanded to witness, (Matthew 28:19), and we are commanded to ask, to seek, and to knock, (Mt 7:7-8). Ask the Lord for His soon return, and then go out into this fine day and share the Good News. Who knows, the person you lead to Christ might just be the one destined to complete the number, and then the ship will sail!