iOS Gospel Library uses iOS' built-in mechanism for selecting text, which doesn't support re-selecting a group of words (i.e. the bounds of the highlight) when tapping (I think it's a "security feature" that iOS doesn't allow apps to select text on a page on behalf of the user – the user has to initiate text selection by long-pressing and dragging). The workaround is to create a custom text-selection feature, which is possible, but it may introduce bugs, and as the OS changes it will need to be kept up-to-date to make sure the look and feel matches iOS' native text selection (if that's possible at all). So, it's an iOS limitation, but there are workarounds, but those workarounds are "scary."
Samuel Bradshaw • If you desire to serve God, you are called to the work.