Final answer:
First Clement was considered orthodox because of its condemnation of Marcion.
Step-by-step explanation:
First Clement was considered by some Christians to be:
- Heretical because of its docetic Christology
- Orthodox because of its rejection of clergy
- Orthodox because of its condemnation of Marcion
- A part of the New Testament
Based on the information provided, the correct answer is option 3. First Clement was considered orthodox because of its condemnation of Marcion. Marcion was a second-century Christian leader who promoted his own form of Christianity and was considered a heretic by the early church. First Clement's condemnation of Marcion aligns with mainstream Christian beliefs, making it an orthodox text.