The Talmud cites the verse, “Then you will come to see the difference between he who serves God and he who does not serve Him” and asks what the point of difference is between one who serves God and one who does not.
Our sages explain that one who does not serve God repeats his study of the same chapter a hundred times, whereas one who serves God repeats his study of the chapter a hundred and one times.
Can it be that a difference of one time turns a person from one who does not serve God into one who serves Him?
To answer this question, the Talmud cites Hillel the Elder: “Go and learn from the mule-drivers’ market.”
It costs one zuz to rent a mule for a distance of ten parasangs (31/2 miles), but a distance of eleven parasangs costs twice as much.
Because the eleventh parasang exceeds the distance the mule is used to traveling.
Of course, not many people review their studies a hundred times, and that itself is certainly a high level.
Yet one who reviews something a hundred times remains within a certain limit; this suffices him, and he gets into a certain routine.
By contrast, one who reviews his chapter a hundred and one times breaks this limit.
The hundred-and-first time is important not because it is one more time, but because it indicates that the person does not allow himself to fall into a routine, a habit of study.
In other words, the central point is that of breaking the routine.
–Rabbi Adin Steinsaltz