Parable Books has just closed their online digital bookstore and will no longer be selling eBooks. The Christian company has declared that their users had three days to backup their past purchases, so they can continue to read them on other devices, if you missed the October 31st cutoff, you are out of luck.
Parable is a brick and motor chain of Christian Book Stores and they experimented with eBooks two years ago. If a customer wanted to support their nearest location, they could buy eBooks and by using a special referral code, the store would get a small commission.
If you are still looking for religious eBooks there are plenty of stores that still sell them Christianbook is one of the largest one that I know of and they are still in business. Lifeway sells ebooks and is a relatively big chain (and is the retail arm of B&H Publishing), but the digital content only works with their own apps. Also, a bunch of Christian publishers sell their own eBooks directly, though (Crossway, Ignatius Press, New Leaf Publishing.
The closure of Parable really drives home the fact that there is no clear path of ownership when you purchase eBooks. You are merely paying for a limited license that could be suspended at any time. This is one of the pitfalls of purchasing eBooks, they can disappear at a moments notice.