The download button opens the iTunes App Store, where you
may continue the download process. You must have iTunes installed with an
active iTunes account in order to download and install the software. This
download may not be available in some countries.
From David Butler:
Christian books can be expensive, and it's quite likely that someone else in your church family already has the book you're interested in reading and would be willing to lend it to you. Or, you might have a book that someone else would like to read. This app lets you list (and scan in via the barcode reader) the books you own and would like to read to create a virtual library so you can lend and borrow books.