In the second century C.E., a man named Marcion received people’s attention (and the attention of the church) when he denied the importance of the Old Testament. He claimed that Old Testament books might have been inspired by God, but that the Old Testament God was inferior to the New Testament God. Also, he denied Jesus’ humanity, going so far as to excise all references to Jesus’ incarnation and suffering in the small canon he developed. Marcion’s increasing popularity spurred the church to decide in earnest which scriptures should be in the New Testament canon.

In the fourth century C.E., Eusebius of Caesarea was asked by Emperor Constantine to come up with a standard Bible. As Eusebius pored over the wealth of Christian writings, he learned about what writings had been accepted by various churches. By determining which writings were most widely accepted and which were least accepted, Eusebius developed a standard by which he judged the writings canonical or not. The framework of this standard was used in the final canonization of the Bible.

Athanasius, a contemporary of Eusebius, was the Bishop of Alexandria. The first known reference to a list that mirrors the New Testament canon as it is known today appeared in his Easter letter to Christians in 367 C.E.. In the letter, Athanasius declared that some Christian writings should be read as Holy Scripture; other writings were suitable for understanding the faith, but should not be classified as holy.