Justin Martyr in the context of "Early Christian writers"

An apologia (Latin for apology, from Ancient Greek: ἀπολογία, lit. 'speaking in defense') is a formal defense of an opinion, position or action. The term's current use, often in the context of religion, theology and philosophy, derives from Justin Martyr's First Apology (AD 155–157) and was later employed by John Henry Newman's Apologia Pro Vita Sua (English: A Defense of One's Own Life) of 1864, which presented a formal defense of the history of his Christian life, leading to his acceptance by the Catholic Church in 1845.

In Ancient Greece, an apologia was primarily used as a legal defense: The accuser would present a kategoria, or accusation, and the defendant would present his apologia, or defense. In modern usage, apologia describes a formal defense of an idea or belief, rather than against a legal charge. In both ancient and modern uses it differs from an apology, or expression of regret. The main difference between the two is that the act of apologizing is meant to express regret, and the purpose of an apologia is to clearly communicate the rational grounds for a belief or position. As an example, a person might apologize for bumping into another person, but could write an apologia to explain why they believe a specific belief is superior to another specific belief.

Christian apologetics (Ancient Greek: ἀπολογία, "verbal defense, speech in defense") is a branch of Christian theology that defends Christianity.

Christian apologetics have taken many forms over the centuries, starting with Paul the Apostle in the early church and Patristic writers such as Origen, Augustine of Hippo, Justin Martyr and Tertullian, then continuing with writers such as Thomas Aquinas, Duns Scotus, William of Ockham and Anselm of Canterbury during Scholasticism.

Mystery religions, mystery cults, sacred mysteries or simply mysteries (Greek: μυστήρια), were religious schools of the Greco-Roman world for which participation was reserved to initiates (mystai). The main characteristic of these religious schools was the secrecy associated with the particulars of the initiation and the ritual practice, which may not be revealed to outsiders. The most famous mysteries of Greco-Roman antiquity were the Eleusinian Mysteries, which predated the Greek Dark Ages. The mystery schools flourished in Late Antiquity; Emperor Julian, of the mid-4th century, is believed by some scholars to have been associated with various mystery cults—most notably the mithraists. Due to the secret nature of the schools, and because the mystery religions of Late Antiquity were persecuted by the Christian Roman Empire from the 4th century, the details of these religious practices are derived from descriptions, imagery and cross-cultural studies.

Justin Martyr in the 2nd century explicitly noted and identified them as "demonic imitations" of the true faith; "the devils, in imitation of what was said by Moses, asserted that Proserpine was the daughter of Jupiter, and instigated the people to set up an image of her under the name of Kore" (First Apology). Through the 1st to 4th century, Christianity stood in direct competition for adherents with the mystery schools.

Celsus (/ˈsɛlsəs/; Hellenistic Greek: Κέλσος, Kélsos; fl. AD 175–177) was a 2nd-century Greek philosopher and opponent of early Christianity. His literary work The True Word (also Account, Doctrine or Discourse; Greek: Hellenistic Greek: Λόγος Ἀληθής) survives exclusively via quotations in Contra Celsum, a refutation written in 248 by Origen of Alexandria. The True Word is the earliest known comprehensive criticism of Christianity and Judaism.

Hanegraaff has argued that The True Word was written shortly after the death of Justin Martyr (who was possibly the first Christian apologist), and was probably a response to his work. Origen stated that Celsus was from the first half of the 2nd century AD, although the majority of modern scholars have come to a general consensus that Celsus probably wrote around AD 170 to 180.

The First Apology was an early work of Christian apologetics addressed by Justin Martyr to the Roman Emperor Antoninus Pius. In addition to arguing against the persecution of individuals solely for being Christian, Justin also provides the Emperor with a defense of the philosophy of Christianity and a detailed explanation of contemporary Christian practices and rituals. This work, along with the Second Apology, has been cited as one of the earliest examples of Christian apology, and many scholars attribute this work to creating a new genre of apology out of what was a typical Roman administrative procedure.

A Christian Hebraist is a scholar of Hebrew texts who approaches the works from a Christian perspective. The main area of study is the Hebrew text of the Bible (known as the Old Testament to Christians and as the Tanakh to Jews), but Christians have occasionally taken an interest in the Talmud and the Kabbalah.

The discipline has long been a site of Jewish–Christian intellectual interaction. The early church fathers got their knowledge of Hebrew traditions (Masoretic, Midrashim and Aggadah) from Jewish teachers. That is seen especially in the exegesis of Justin Martyr, Aphraates, Ephraem Syrus and Origen of Alexandria. Jerome's teachers are even mentioned by name such as Bar Ḥanina (Hananiah). In the Middle Ages, Christian converts from Judaism provided a key source of Hebrew education, as native Christians rarely learned the language. As the Renaissance and Enlightenment proceeded, the discipline increasingly came to investigate extrabiblical texts, and eventually became a branch of philology.