When we study the book of Jude in our Bible study group, I found that in verse 9 and verse 14, Jude quoted "The Lord rebuke thee" and "Behold, the Lord cometh with ten thousands of his saints," but they were not in the Old Testament. A brother told me that they are in the Catholic's Apocrypha. If it is true, I cannot understand why Jude quoted sentences from an apocrypha, because we believe they are not God's word. And how did the Christians in the past decided which book should be in the Bible, which book should not? And why did they have a different opinion with the Catholics?
"Yet Michael the archangel, in contending with the devil, when he disputed about the body of Moses, dared not bring against him a reviling accusation, but said, "The Lord rebuke you!"" (Jude 9).
"Now Enoch, the seventh from Adam, prophesied about these men also, saying, "Behold, the Lord comes with ten thousands of His saints, to execute judgment on all, to convict all who are ungodly among them of all their ungodly deeds which they have committed in an ungodly way, and of all the harsh things which ungodly sinners have spoken against Him" (Jude 14-15).
Often times confusion comes from our assumptions instead of what is actually stated. Please notice that you assumed that these two quotes came from written documents. Why? Jude did not say "It is written," or some similar statement. He stated what was said. How could he know? The simplest assumption is that the Holy Spirit told Jude what had happened and what was said.
What should also be noted is that we don't have evidence that these statements pre-existed Jude's letter. There is a book called I Enoch which contains a line roughly similar to Jude 14-15. The problem is that the only copy that contains this line dates 1700 years after Jude. I Enoch did exist prior to Jesus; we've found fragments of it among the Dead Sea scrolls. However, the book was never accepted by the Jews as inspired, the fragments we have don't contain Jude's quote, and those fragments don't match the one whole Ethiopian translation of I Enoch that we do have. What cannot be ruled out is that these statements in Jude were added after the fact to the existing fable known as the Book of Enoch. See "Why don't you use the Book of Enoch?" for more details and why I Enoch fails the tests for inspired writings.
I Enoch, by the way, is not accepted by the Catholic church as an inspired book, so the statements in Jude are not found among the Catholic's apocrypha.