I love the variety in this list. These Bible studies will challenge believers at any point in their walk. They range from Little Thoughts About a Big God, which is more of a collection of daily devotional thoughts and stories (a great stocking stuffer for believers and non believers), to Seamless (takes you from Genesis to Revelation in 8 weeks, great for a new believer...but I learned a TON from it the first time I did it and I had been a believer for 25 year at that point), to the others that are solely on Scripture and going deep into the text itself. All of these books will help you learn more about the Bible and allow you to understand Jesus and his commands in a deeper way.
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Little Thoughts About a Big God- Rob James
Unexplainable Life- Erica Wiggenhorn
Unexplainable Church- Erica Wiggenhorn
Unexplainable Jesus- Erica Wiggenhorn
Seamless- Angie Smith
Flourish- Passion City Church
Patriarchs- by Beth Moore