There are four areas to check to determine of a source is generally reliable. They are 1) Dates 2) Manuscripts 3) Archaeology and 4) Non-Biblical Sources.
1. Dates – when was the document written in relation to the event. If it was written relatively close to the event, then this gives the possibility of being historically reliable. The area of dating asks the question “when was the New Testament written?” Especially the gospels. If they were written in the 1st century (the same century Jesus lived), then that is within the lives of the eyewitnesses which is what a historian desires for reliability.
“New Evidence the Gospels were Based on Eyewitness Accounts” by Peter J. Williams at bethinking.org
2. Manuscripts – Concerning manuscripts there are no original documents (called “autographs”) of any book of the New Testament. In order to reproduce what was in the original you have to compare and contrast the varied manuscripts (copies). The more manuscripts you have the better you can reproduce the original autograph.
“‘Misquoting’ Jesus? Answering Bart Erhman” Greg Koukl in Solid Ground (pdf)
“Is What We Have Now What They Wrote Then” by Daniel Wallace Bible.org
“No ‘Lost’ Books of the Bible” by Greg Koukl in Solid Ground (pdf)
For a more extensive discussion on the transmission process of the New Testament check out:
Impact 360 has a great video summarizing the three questions about the manuscript evidence of the New Testament: 1. How many copies exist? 2. How large is the time gap? and 3. How significant are the differences?
3. Archaeology – Archaeology is a way to cross check the New Testament with artifacts. Since the New Testament discusses places, locations, rules and reigns, even specific descriptions of buildings, it would be reasonable to expect archaeological evidence to confirm many of these events, locations, and even buildings.
“Archaeology and the Bible” – Eric MeTaxas The Christian Post
Christian scholars are so confident in the historical reliability of the Bible they have produced the Archaeological Study Bible which provides the historical context of the Bible. Full of informative articles and full-color photographs of places and objects from biblical times, this Bible examines the archaeological record surrounding the text. It provides informed about the empires, places, and peoples of the ancient world.
4. Non-Biblical Sources – Sources outside of the Bible can act as corroborating source. Just like an eyewitness can help justify the defendant’s testimony, sources outside the bible can help corroborate the narrative inside the scriptures.
“Ancient Evidence for Jesus from Non-Christian Sources” by Michael Gleghorn at BeThinking.com
“Did Jesus Exist? Searching for Evidence Beyond the Bible” by Lawrence Mykytiuk at Biblical Archaeological Review
“Is There Any Evidence for Jesus Outside the Bible?” by J. Warner Wallace at coldcasechristianity.com