What is the difference between the prophecy books of the New and Old Testaments?

According to the Bible... the difference between the Old Testament prophecies and the New is the coming of the Messiah.

Until Jesus Christ came at the time of the end of God's plan: "...the Words are closed up and sealed till the time of the end... none of the wicked shall understand; but the wise shall understand." (Dan.12:9-10)

The "parable" of the book of Revelation, however, illuminates and reveals the meaning of the closed up and sealed prophecies... [to the understanding of God's servants -- the "end time wise": the "fear of the Lord" is the beginning of "wisdom" - Prov.9:10].

"The Revelation of Jesus Christ, which God gave unto Him, to shew unto His servants... Blessed is he that readeth, and they that hear the Words of this prophecy, and keep those things which are written therein: for the time is at hand." (Rev.1:1-3)

Until Jesus Christ came, along with the understanding of the Holy Spirit:

"...no man was found worthy to open and to read... [to understand -- the prophecies]... neither to look thereon." (Rev.5:4)

With the advent of Jesus Christ, however: "... the Lion of the tribe of Juda, the Root of David, hath prevailed to OPEN THE BOOK, and to LOOSE THE SEVEN SEALS THEREOF. (verse 5)

"...they sung a NEW SONG, saying, Thou art worthy to take the book, and to open the seals thereof: for thou wast slain,, and hast redeemed us to God by thy blood out of every kindred, and tongue, and people, and nation; and hast made us unto our God kings and priests: and we shall reign on the earth." (verses 9-10)

It is Jesus Christ who brings "spiritual understanding" to the closed and sealed prophecies of old.

It's Jesus Christ who elevates the "letter of the law" to a "spiritual plane."

"...Seal not the sayings of the prophecy of this book: for the time is at hand. He that is unjust [the end time wicked of Daniel 12:10], let him be unjust still: and he which is filthy, let him be filthy still: and he that is righteous [the end time wise of Daniel 12:10], let him be righteous still: and he that is holy, let him be holy still.

"And, behold, I come quickly; and My reward is with Me, to give every man according as his work shall be." (Rev.22:10-12)