Do Unitarians generally believe in the same # of books as Catholics/Protestants?
Modern unitarians usually follow the Protestant bible, as modern Unitarianism is a branch of Protestantism from the Enlightenment period. However, it's roots go back much further than the 18th century. Here are some examples of various unitarian sects throughout the centuries, and their biblical canon:
The Ebionites and Nazarenes
The Ebionites are considered by secular historians to have been the first and original branch of Christianity. Their canon included the Hebrew Scriptures, as well as a Hebrew (or Aramaic) version of Matthew; believed by some to be the original gospel that Matthew wrote. Their copy of Matthew did not include the first two chapters, and it is unknown if they rejected the virgin birth, or if they just never heard of it. They also rejected any of Paul's letters, believing him to be a false apostle.
The Nazarenes were a similar sect of the same period. Some did accept a virgin birth, though it is often believed "Nazarenes" is just another name for the Ebionites. They were also unitarian and believed Yeshua was a spectacular man. Interestingly, some historians believe Yeshua was a prominent memeber of this sect. It's possible the Nazarenes were the same branch as the Nazarenes of the Judaic Essenes, seeing that there is no evidence of a city called Nazareth in the 1st century, and the Essenes are never mentioned in the gospels. Because of this, some scholars believe there was no "Jesus of Nazareth", but rather "Jesus the Nazarene".
The Early Church
Artemon and Theodotus of Byzantium were some of the earliest unitarians relevant to the early church. They taught that Yeshua was a man, and Eusebius says in one of his propaganda works: 1
They do not endeavor to learn what the Divine Scriptures declare, but strive laboriously after any form of syllogism which may be devised to sustain their impiety. And if any one brings before them a passage of Divine Scripture, they see whether a conjective or disjunctive form of syllogism can be made from it. And as being of the earth and speaking of the earth, and as ignorant of him who cometh from above, they forsake the holy writings of God to devote themselves to geometry. Euclid is laboriously measured by some of them; and Aristotle and Theophrastus are admired; and Galen, perhaps, by some is even worshiped.
Paul of Samosata was a bishop in the late 200's AD. Although all his work has been destroyed, we know that he taught Yeshua was a man. It is unclear what his biblical canon was, but we know he believed in a virgin birth and accepted the letters of Paul.
During the Refmormation, many new and old idea were being presented. Although Michael Servetus may have believed in a form of Arianism rather than unitarianism, he is regarded by many Unitarian sects as their first martyr. Servetus was a polymath who studied the Scriptures in their original language. He accepted the virgin birth and the letters of Paul, but publicly denied the trinity, which led to his burning on a stake under the recommendation of John Calvin.
After Servestus there was a sect called Socinianism, named after their founder Fausto Sozzin. Sozzin accepted the Protestant canon, believed in the virgin birth, and accepted Paul's letters. However, unlikely Servetus, he denied any sort of "preexisting christ".
The Enlightenment, like the Reformation, saw many new ideas being presented. There was a fairly large unitarian movement happening during this time, and the first unitarian denomination was established by Theophilus Lindsey. With the help of polymath and chemist Joseph Priestley, the unitarian church spread throughout Europe. Priestley wrote many books during this period, including A History of the Corruptions of Christianity. Although Priestley accepted the letters of Paul, he denied the virgin birth and a preexistant Messiah. Thomas Jefferson, who is considered a unitarian deist and rejected the letters of Paul, wrote to John Adams: 2
You are right in supposing, in one of yours, that I had not read much of Priestley’s Predestination, his No-soul system, or his controversy with Horsley. but I have read his Corruptions of Christianity, & Early opinions of Jesus, over and over again; and I rest on them, and on Middleton’s writings, especially his letters from Rome, and to Waterland, as the basis of my own faith. these writings have never been answered, nor can be answered, by quoting historical proofs, as they have done. for these facts therefore I cling to their learning, so much superior to my own.
Do they simply re-interpret verses in the NT or do they reject certain verses?
Unitarians do interpret many verses differently than triniatarians, modalist, and Arians, but the scope of this would be too large to cover here. If you have any questions about a verse, please ask a separate question so answers can deal with the specific problem.
Some unitarians reject the first two chapters of Matthew and Luke, believing them to be inconsistent with the gospels, lacking archaeological evidence, and of a pagan origin. Some unitarians also deny Paul as an apostle or having any sort of authority, believeing his conversion to be inconsistent with the human Messiah and accusing Paul of docetism.
I can only think of two relevant verses that most unitarians outright reject. Quotes are from the KJV (a Protestant bible):
"For there are three that bear record in heaven, the Father, the Word, and the Holy Ghost: and these three are one." 1 John 5:7
The bolded area is generally rejected by all newer translations, and seems to have popped up sometime during the 1600's. It was also a reason for Issac Newton's rejection of the trinity after he read the original Greek manuscripts of his time.
"Saying, I am Alpha and Omega, the first and the last: and, What thou seest, write in a book, and send it unto the seven churches which are in Asia; unto Ephesus, and unto Smyrna, and unto Pergamos, and unto Thyatira, and unto Sardis, and unto Philadelphia, and unto Laodicea." Revealtion 1:11
Again, modern translations usually reject the bolded quote. This is the resurrected Yeshua speaking to John, and would definitely provide evidence that Yeshua was claiming to be God, but this verse is absent from all of the oldest manuscripts. 3
Unitarians find it suspicious that these words were added to the Greek manuscripts and accepted in English translations, and usually consider this further evidence that a lack of biblical support for trinitarianism has caused these verses to be included.
The biblical canon for unitarians has varied over the centuries. Most accept the Protestant canon and only reject those verses which mainstream Christian scholars have determined to be corruptions.
- Eusebius of Caesarea, Ecclesiastical History Book v. Chapter xxviii
- Thomas Jefferson to John Adams, 22 August 1813
- Commentaries on Revelation 1:11