Death was not introduced to the world as a punishment. Rather, it was a secondary and easier way for a person to achieve the World to Come. Every minute of our lives we are involved in a process of either holiness or purification, as G-d tests us to see what we will do. The test levels for each type of person are different; while one person may be tested to see if he will uphold all the mitzvos, another's test may be to see if he will retain even the tiniest scrap of his Judaism or if he will let it all fall behind him. As time goes on and we become purer and purer, we are then entitled to know deeper parts of the Torah and they become within our reach.