The 2nd century apostolic writers had a loose connection to the original apostles. Some of these early 2nd century writings were occasionally considered part of the canonical biblical writings. This post-apostolic group lived after the destruction of the Jerusalem Temple in 70 CE. These authors included Clement of Rome (40-101 CE) and his writings, as well as the so-called Second Letter of Clement, a 2nd century sermon, but not from Clement. There also was Ignatius of Antioch (50-117 CE) with his letters, and the 2nd century Pseudo-Barnabas letter. From the late 1st century, the Didache, the Teaching of the Twelve Apostles, has intrigued scholars. The 2nd century Shepherd of Hermas, has an apocalyptic document that included visions, commands, mandates, and parables or similitudes. Theophilus of Antioch (115-180 CE) and Melito of Sardis (+190 CE), an important bishop of Asia Minor, were writing apologists for Christianity. Clement of Alexandria (150-215 CE) and his pupil Origen (185-254 CE) played an important role in the developing Christian theology in Alexandria. Justin the martyr (100-165 CE) gave a great description of the Christian activities. Irenaeus (140-202 CE), a disciple of the martyr Bishop Polycarp of Smyrna, wrote against various early Christian heretics.
There are fourteen Pauline epistles, letters generally attributed to the apostle Paul. The Greek name for a letter was epistle (ἐπιστολὴ). Nine of these Pauline epistles were addressed to seven Christian Churches that he had visited. 1 Thessalonians, from the early 50s CE, is perhaps the oldest document of the New Testament. 2 Thessalonians dates from the early to late 60s CE. The letter to the Romans was composed between 53-57 CE. 1 Corinthians and 2 Corinthians date from 53-57 CE also. The letter to the Galatians comes from the late 50s CE), while the letter to the Colossians dates from the late 50s to the early 60s CE. The letters to the churches of the Ephesians and the Philippians comes from the early 60s CE. A lot of Christian theology has been based on the reflections of these letters that were describing what was happening in their early Christian communities.