[Just before Moses' death] God said to him, "This is the Land that I promised to Abraham, to Isaac, and to Jacob" (Deuteronomy 34:4).
The Midrash says that Moses pleaded to live long enough to be able to enter the Promised Land. He surrendered his soul only after God instructed him to enter Heaven and inform the Patriarchs that the Israelites had come to their Land and that God had indeed fulfilled His promise to give the Land of Israel to their descendants. To fulfill God's will was dearer to Moses than his craving to enter the Land.
It is only natural to cling to life, and the thought of leaving this world is depressing. However, if a person develops the attitude that he lives only in order to fulfill God's will, then life and death are no longer polar opposites, because he lives to do the will of God, and when that will requires that he leave this world, he will be equally obedient.
The seventh day of Adar is the anniversary of Moses' death. He wanted to enter the Promised Land so that he could fulfill the commandments and thereby have a new opportunity to fulfill the Divine wish. He surrendered his soul willingly when he was told that there was a special commandment for him to perform, one that could only be achieved after leaving this earth.
We refer to Moses as Rabbeinu, our teacher. He not only taught us didactically, but by means of everything he did in his life - and by his death, as well.