I have been studying the writings of early Christians like Justin Martyr and Ignatius. I know their writings are not inspired or biblical, but can we use them as examples in any way? Also in Ignatius' writings I see the word Catholic. What does it mean?
The word "catholic" is a Latin-based word that means "universal." The early Christians writers used it to refer to the church as a whole across the world, as opposed to a local church.
Early Christian writers should be treated as any other uninspired writer. It is interesting to see what their understanding of the Scriptures were, but we must always keep in mind that they might be (and sometimes were) wrong on various issues. But just as we read modern writers to get their take on biblical subjects, so we can use the early Christian writings.
The writers are useful from a historical prospective. We can see their use of the Bible, especially their heavy quoting of the Scriptures makes for another source in finding copyist mistakes and to see that the books of the Bible were considered inspired source material. Some of the writers personally knew the apostles, so they add another dimension to the historical accuracy of the Bible.
Through the early writers we can also trace the deviation from the teachings of the Scriptures; thus, we can see the path taken that led to a hierarchical system with a separate clergy and laity.
Sometimes there are arguments regarding the meaning of words in Koine Greek. Since these men spoke that particular dialect, their explanations help clarify the meaning of various words.