Chazal instituted the reading of Parshas Ki Savo before Rosh Hashana. Much of the parsha deals with the terrible consequences for not observing the Torah. We read this prior to Rosh Hashana symbolizing that the year and all its curses should come to an end. In reality, we do not read Parshas Ki Savo immediately before Rosh Hashana, but rather there is always a Shabbos after Ki Savo before the year ends. If we want to indicate that the year and its curses are ending, wouldn't it be more appropriate to read this parsha on the last Shabbos of the year? Why did Chazal leave a week between Parshas Ki Savo and Rosh Hashana?
We are taught (Berachos 5a) various methods to overcome one's yetzer hara. If one senses a temptation to sin one should first focus on words of Torah. If this doesn't help, one should recite the Shema. If even this fails to assist in overcoming one's yetzer hara, as a last resort one should focus on death. If thinking about death is the most effective way to prevent one from sinning, why didn't Chazal suggest this as the first response to temptation? Why do we first attempt the less effective deterrents such as Torah study and krias Shema?
When a person is ill there are often different potential treatments. Sometimes a more effective one will not be used at first because of its negative side effects. If the less effective cure is not sufficient and the condition necessitates, the illness must be cured notwithstanding the damaging side effects. Thinking of death is the most effective way of averting sin. However, using this as a constant deterrent can have negative repercussions. A person constantly focused on death will not be able to serve Hashem with joy. His morose mood will prevent him from interacting with others in a cheerful and pleasant way. Thinking of death as a first response to every temptation may be effective in preventing a particular sin, yet it may carry negative consequences that outweigh its benefits. Only if the gentler methods of Torah study and krias Shema fail should one resort to the more drastic approach of focusing on death.
As we approach Rosh Hashana and try to perfect our avodas Hashem, we have many methods that we use. We increase our Torah study and focus on kabbalos Malchus Shomayim - accepting Hashem's kingship over us through our tefillos. There is a last method that we use and that is reflecting upon deaths. Perhaps the most powerful application of this is the tefillah of Unesane Tokef. Yet, the majority of our tefillos on Rosh Hashana focus on Hashem being our King, rather than our own mortality. The mood on Rosh Hashana is both serious and joyful. Constant focus on death would perhaps prevent sin but would also prevent us from celebrating Rosh Hashana appropriately.
During the weeks before Rosh Hashana we prepare our different strategies for overcoming sin. We deliberately do not enter Rosh Hashana on a depressing note having just read the curses of Parshas Ki Savo. Death and suffering are not the methods we want to invoke as we attempt to improve our avodas Hashem. We have these methods available to us in case of need. We read about them two weeks before Rosh Hashana to familiarize ourselves with them, but then have a break of a week so that they do not preoccupy our minds. We approach Rosh Hashana using the methods of Torah study and krias Shema - accepting Hashem as King - as ways of combating sin. If and when we must resort to contemplating death as a way to assist us we are equipped to do so. Parshas Ki Savo can be invoked if necessary but we hope that Torah study and krias Shema can assist us as we strive to perfect our avodas Hashem.