Enoch was a great prophet who "walked with God." We first read about him in Genesis 5:18-24.
"And Jared lived 162 years, and he begat Enoch. And Jared lived after he begat Enoch 800 years and he begat sons and daughters. All the days of Jared were 962 and he died. And Enoch lived 65 years and begat Methuselah. And Enoch walked with God after he begat Methuselah, 300 years, and he begat sons and daughters. All the years of Enoch were 365. And Enoch walked with God, and he was not, for God took him."
Then in Hebrews 11:5, the writer speaks of Enoch.
"By faith, Enoch was translated that he should not
see death; and was not found because God had
translated him, for before his translation, he had this testimony...that he pleased God."
The name "Enoch" in Hebrew is "hanokh", which means "consecrated." Certainly Enoch consecrated his life to the Lord.
His life began 65 years before Methuselah was born, and yet he has not died. Enoch was raptured, and taken from this earth alive 69 years before Noah was born.
The book of Jude quotes from the book written by Enoch. (vv.14-15)
"And Enoch also, the seventh from Adam, prophesied of these saying, 'Behold, the Lord comes with ten thousands of His saints. To execute judgment upon all, and to convince all that are ungodly among them of their ungodly deeds, which they have ungodly committed, and of all their hard speeches which the ungodly sinners have spoken against Him.'"
This "Book of Enoch" was known to the early church.
Not only did Jude quote from it (showing not only his validation of the book, but also that God validated it by including it into the Holy Word); but Origen and Tertullian and others in the early church mentioned this book by name. For many centuries this book of Enoch was read and enjoyed.
Where in the Bible would Jude have gotten that information on what and how Enoch preached ?
It is in the Book of Enoch, which was used by the early church for the first 300 years. In the forming of the Roman Catholic church it was removed, for Jerome and Augustine did not like the story of the fallen angels going in unto women of the earth, and making a race of giants... They could not get the council to vote it was not 'Scripture' though,
so they had them choose between the Book of Enoch and the Book of Revelation, saying the Bible was too big already for both to be in...