It simply is not called this. The Book of Isaiah is called this as it is the most quoted/referred/implied book in the New Testament.
As for Christians, the concluding book is called Revelation.
Revelation
REVELATION The last book in the Bible is "The Apocalypse", commonly now known as "The Book of Revelation" or casually as "Revelations". It was written by St. John.
The last book in the Bible is called Revelation or the Revelations of St. John.
The writing in Revelation is called apocalyptic
Most of the Book of Revelation deals with the end times.
Book of Isaiah
The last book of the Holy Bible is Revelation.
check again... it is the last book of the Bible!
Pure Bible Study - 2010 Revelation 101 Introduction to the Book of Revelation Bible Study was released on: USA: 29 December 2010
The last book is revelation
The Book of Revelation