The Bible refers to collections of sacred scripture of Judaism and Christianity. There is no single version: both the individual books (Biblical canon) and their order vary. The Hebrew Bible contains 39 books, while Christian Bibles range from the 66 books of the Protestant canon to 81 books in the Ethiopian Orthodox Bible. The oldest surviving Christian Bibles are Greek manuscripts from fourth century AD; the oldest Hebrew manuscripts date from the Middle Ages.

The Hebrew Bible, or Tanakh, is divided into three parts: (1) the five books of the Torah ("teaching" or "law") comprise the origins of the Israelite nation and its covenant with God; (2) the Nevi'im ("prophets") containing the historic account of ancient Israel and Judah plus works of prophecy; and (3) the Ketuvim ("writings"), poetic and philosophical works such as Psalms and Job. Christian Bibles include the books of the Hebrew Bible, but arranged in a different fashion: Hebrew Scripture ends with the people of Israel restored to Jerusalem and the temple and the Christian arrangement ends with the book of the prophet Malachi.

The Christian Bible is divided into two parts. The first is called the Old Testament, containing the 39 books of Hebrew Scripture, and the second portion is called the New Testament, containing 27 books. Soon after the establishment of Christianity in the first century, Church Fathers compiled Gospel accounts and letters of apostles into a Christian Bible which became known as the New Testament. The Old and New Testaments together are commonly referred to as "The Holy Bible". The canonical composition of the Jewish Bible is in dispute between Christian groups: Protestants hold only the books of the Hebrew Bible to be canonical; Roman Catholics and Eastern Orthodox additionally consider the deuterocanonical books, a group of Jewish books, to be canonical. The New Testament is composed of the Gospels ("good news"), the Acts of the Apostles, the Epistles (letters), and the Book of Revelation. The Bible is the best-selling book in history with approximate sales estimates ranging from 2.5 billion to 6 billion.

According to the Online Etymology Dictionary, the word Bible is from the Latin biblia, traced from the same word through Medieval Latin and Late Latin, as used in the phrase biblia sacra ("holy book")—"In the Latin of the Middle Ages, the neuter plural for Biblia (gen. bibliorum) gradually came to be regarded as a feminine singular noun (biblia, gen. bibliae in which singular form the word has passed into the languages of the Western world.") This stemmed from the Greek term τ? βιβλ?α τ? ?για (ta biblia ta hagia), "the holy books", which derived from βιβλ?ον (biblion), "paper" or "scroll," the ordinary word for "book", which was originally a diminutive of β?βλος (byblos, "Egyptian papyrus"), possibly so called from the name of the Phoenician port Byblos (also known as Gebal) from whence Egyptian papyrus was exported to Greece.

The Greek phrase Ta biblia (lit. "little papyrus books") was "an expression Hellenistic Jews used to describe their sacred books several centuries before the time of Jesus," and would have referred to the Septuagint. The Online Etymology Dictionary states, "The Christian scripture was referred to in Greek as Ta Biblia as early as c.223."

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A catechism ( /ˈkatəˌkɪzəm/; from Ancient Greek: κατηχέω, "to teach orally") is a summary or exposition of doctrine and serves as a learning introduction to the Sacraments traditionally used in catechesis, or Christian religious teaching of children and adult converts. Catechisms are doctrinal manuals – often in the form of questions followed by answers to be memorised – a format that has been used in non-religious or secular contexts as well. According to Norman DeWitt, the early Christians appropriated this practice from the Epicureans, a school whose founder Epicurus had instructed to keep summaries of the teachings for easy learning. The term catechumen refers to the designated recipient of the catechetical work or instruction. In the Catholic Church, catechumens are those who are preparing to receive the Sacrament of Baptism. Traditionally, they would be placed separately during Holy Mass from those who had been baptized, and would be dismissed from the liturgical assembly before the Profession of Faith (Nicene Creed) and General Intercessions (Prayers of the Faithful).

Catechisms are characteristic of Western Christianity but are also present in Eastern Orthodox Christianity. In 1973, The Common Catechism, the first joint catechism of Catholics and Protestants, was published by theologians of the major Western Christian traditions, as a result of extensive ecumenical dialogue.

Format

Before the Protestant Reformation, Christian catechesis took the form of instruction in and memorization of the Apostles' Creed, Lord's Prayer, and basic knowledge of the sacraments. However there were also more comprehensive documents that outlined of the Christian faith, such as the Catechetical Lectures of St. Cyril of Jerusalem, "The Morals" of St. Basil of Caesarea, and the Enchiridion on Faith, Hope and Love by St. Augustine of Hippo. The earliest known catechism is the Didache, which was written between 60 and 85 AD.

The word "catechism" for a manual for this instruction appeared in the Late Middle Ages. The use of a question and answer format was popularized by Martin Luther in his 1529 Small Catechism. He wanted the catechumen to understand what he was learning, so the Decalogue, Lord's Prayer, and Apostles' Creed were broken up into small sections, with the question "What does this mean" following each portion. The format calls upon two parties to participate, a master and a student (traditionally termed a "scholar"), or a parent and a child. The Westminster Shorter Catechism (1647) is an example:

Q. What is the chief end of man?

A. To glorify God and enjoy Him forever!

Q. What rule hath God given to direct us how we may glorify and enjoy Him?

A. The word of God which is contained in the Scriptures of the Old and New Testaments is the only rule to direct us how we may glorify and enjoy him.