שמות טו,יג: נָח יתָ בְחַסְדְךָ עַם־זוּ גָאָלְתָ
The Baal HaTurim comments that the word נחית (guiding) occurs here and in Tehillim (77,21), You guided Your people like a flock.” A shepherd grazes a flock according to the pasture appropriate to it (first he would bring the young kids would graze on the soft new growth; then the mature goats would be brought out to eat the stalks; and finally he brought out the elderly animals to nibble at the stubble and roots.) Also, HaShem had the holy clouds lead the Jews, each according to his pace: the adult taking long strides and the youth according to his smaller stride.
The holy clouds which accompanied the Jews in the desert were seven in number: four on their four sides, one above them, one beneath their feet and one in front of them to guide them. These clouds would lower the heights and raise the depths (so the road would be level); they would also sweep away snakes and scorpions and anything else in the way.
When the clouds leveled the road for the Jews, it was done at different degrees for each individual. For the infirm the road was made smoother; for the robust it left some elevations and depressions. This explains how all the Jews were able to cover the same distance, keeping pace with one another throughout their journey.
