If you look at your list of memory verses you will see a column titled 'eFactor'. This is a number that represents the difficulty (or easiness, hence the name) of memorizing a bible verse. Every time you review a verse, the number is adjusted and over time will be a good measure of how easily you retain that particular memory verse.
The eFactor is one of the biggest determinants of the interval between review sessions. If you keep rating your recall as '5 - Perfect', the eFactor will keep increasing and the interval will grow rapidly. If you rate your recall as '3 - Difficult', the eFactor will decrease and the interval between repetitions will grow slowly. Rating your recall as '4 - Hesitation' will leave the eFactor unchanged and the algorithm will assume that it has the speed with which it is increasing the interval just right.
If this explanation makes your head hurt, don't worry about it. Just think of it as the equivalent of sorting your memory verse flash cards from easy to difficult. The good news is that you don't have to keep track of this yourself and you can leave Memverse to figure it out for you.