I get asked a lot about how to get started studying church history. These are the books I recommend. Also see How to Study Christian History, which gives a plan for learning church history.
To get a quick introduction, here's an excellent starter package:
If you use the links on this page to purchase the books from Amazon, I get a small commission, which helps support this site.
The Ante-Nicene Fathers and specifically volume one and volume two. I cannot overemphasize how important these writings are. If you are going to read any Christian books outside the Bible, you ought to be reading these! These are the writings of those closest in time to the apostles. If you don't read these, you're just guessing at what the apostles taught the churches, and you're just hoping that you've joined the right church and interpreted the Bible correctly.
I have the entire Ante-Nicene Fathers set in paper, on Kindle, and on my computer as .pdf. The Kindle volumes are the most pleasant to read and inexpensive. (Get the "optimized" version so you can read the footnotes). However, I use the .pdf's the most because I can search them if I don't remember where I read something. I had to pay for the .pdf's. You can get them free now.
A lot of people don't question their own interpretation of the Bible. That's sad. It's obvious that millions of Christians, all claiming to be led by the Spirit and honest in their interpretations, have come to many different interpretations of it.
They have then disobeyed and dishonored Christ by dividing over those interpretations, all the while claiming to be sound, spiritual interpreters of the Scripture.
We need guidance. God has promised to reveal truth to the church (1 Tim. 3:15; 1 Jn. 2:27, where each "you" is plural), not to individuals (Heb. 3:13; Eph. 4:13-16; 1 Cor. 12:19-21). From Christian history, you learn what churches throughout the ages believed, and the results they got from their beliefs in joy, unity, and holiness.
It is in this way and not by our own confident interpretations of Scripture that Jesus said to know what is true and whom you can trust (cf. Matt. 7:14-20 and Jn. 5:39-40).
An excellent beginning is to read the writings of the earliest Christians, several of whom were hearers of the apostles, right here on this site. We have taken a number of very early Christian writings, updated the language, and have them available for free reading online.