John Walvoord admitted a "Pretribulation rapture" is not explicitly taught in Scripture.

 A "Pretribulation rapture" is not explicitly or expressly taught in Scripture. Dr John Walvoord (a Pretribulationalist) admitted this more than once, though something caused him to remove this admittance from his first release of his book "The Rapture Question."

"Tribulation" is the designation commonly applied to that 7-year period that the book of Daniel calls a "Week" (Daniel 9:27), and that "Week" is understood by many as the "70th Week of Daniel," because it is the unfulfilled part of a prophecy of which the first 69 weeks have been fulfilled in the past.  The "Rapture" (to be "caught up") is the removal of the "Church," that is, living believers from the earth. A "Pretribulation" rapture view believes this catching up can happen at any moment, but at least before the beginning of the "70th Week."  The end of the 70th Week involves the Second Coming of Christ, and so the pretribulation-rapture-view sees Christ coming for His church before the 70th Week begins.

Dr. John Walvoord was a President of Dallas Theological Seminary and wrote many books on theology, especially on Bible Prophecy, and commentaries on Scripture.  I used to believe as he did on the rapture, but later had a change of mind to the posttribulation-rapture-view.   

I want to point out that Walvoord admitted in his book, 'The Rapture Question," that it was a "fact" that "neither Posttribulationalism nor Pretribulationalism is an explicit teaching of Scripture. The Bible does not state in so many words either."  This statement was removed from later printings of his book.  Why did he do it?  I don't know.  My copy of the book reads differently, it says, "The fact is that posttribulationism is an interpretation of Scripture that pretribulationists believe is contradicted by many passages which imply otherwise." 

There was an accusation by certain parties that Walvoord never admitted to what his first printing (1957) of "The Rapture Question" said, since later copies did not have the statements.  Though that first edition can be found, and photocopies of it are available, I found a similar statement by Walvoord many years later in an article he wrote in the "Grace Theological Journal" (Grace Theological Seminary, Winona Lake, Indiana, Fall 1985).  The article was titled, "Is a Posttribulational rapture Revealed in Matthew 24?"  He wrote: "Both pretribulationists and posttribulationists are confronted with the fact that Scripture does not expressly state either view."  So this statement says essentially the same thing as in the first printing of his book.  So why was the book changed, and yet this article many years later admits the same thing that was removed from the book?   

I would like to point out that if the Apostle Paul got his eschatology (the doctrine of last things / prophecy) from the Lord, and there are obvious parallels between the words of Jesus and Paul on end of the age and the coming of Christ, then there are some strong arguments for a posttribulational rapture.

Consider that Jesus said: 

29 "Immediately after the tribulation of those days the sun will be darkened, and the moon will not give its light; the stars will fall from heaven, and the powers of the heavens will be shaken. 30 Then the sign of the Son of Man will appear in heaven, and then all the tribes of the earth will mourn, and they will see the Son of Man coming on the clouds of heaven with power and great glory. 31 And He will send His angels with a great sound of a trumpet, and they will **gather together His elect **from the four winds, from one end of heaven to the other."

Matthew 24:29-31

Compare this to what Paul said:

"1 Now, brethren, concerning the coming of our Lord Jesus Christ and **our gathering together to Him**"

2 Thessalonians 2:1