Even though the sounding of the shofar on Rosh HaShanah is a decree, it contains an allusion. It is as if [the shofar's call] is saying: “Sleepers, wake up from your sleep, and you who slumber, arise. Inspect your deeds, repent, remember your Creator. Those who forget the truth in the vanities of the moment, who devote their energies all year to vanity and emptiness which will not benefit or save: Look to your souls. Improve your ways and your deeds and let every one of you abandon your evil path and thoughts.”
For these reasons, it is customary for all of Israel to give profusely to charity, perform many good deeds, and be occupied with mitzvot from Rosh HaShanah until Yom Kippur to a greater extent than during the remainder of the year. During these ten days, the custom is for everyone to rise [while it is still] night and pray in the synagogues with heart-rending pleas until daybreak.