Today vast libraries of early Christian material is available online allowing people to research the restorationist beliefs of churches like the Christadelphians to have reclaimed apostolic truth. Here is one such resource.
Christadelphians suggest the help of the Holy Spirit was withdrawn as the New Testament was finish to be replaced by following the completed Bible. This site helps to learn more about how the canon was compiled into its present form and whether this explanation is historically feasible.
The New Testament was written in Greek and many early Christians used the Septuagint (or Greek version) of the Old Testament. This includes New Testament writers as can be shown by analyses of quotations. This has implications for the concept of Biblical infallibility of scripture because the Hebrew and Greek versions have variances. Read the article in the section on the Bible on this site.
Another list of early religious writings.
Simple review of some common methods of interpreting the Bible.
Access ancient Jewish scrolls, discovered in the early twentieth century online which lend light to the accuracy of the Bible and which documents were used at the time.