Gemara:


Ein Ayah: Physical deficiencies will disappear totally when existence will reach its ultimate level of shleimut (completeness). In this world, where we are to progress toward shleimut, there are actually deficiencies that bring on higher levels. In fact, they are irreplaceable in obtaining certain attainments without which the world cannot be sustained.
Three areas that, according to the values of this world, are considered positive things, are: 1) eating and drinking; 2) procreation; 3) commerce. In order that these sustainers of life as we know it will exist, there is a need for negative traits to sustain them.
The existence of eating and drinking and, for that matter, any of a person's needs, requires jealousy. If not for jealousy, no skilled activity would come to fruition and people would not obtain those things that they need. This is the gist of the pasuk: "I saw the toil and the skill of activity, that it is the jealousy of man against his counterpart" (Kohelet 4:4).
Procreation has to do with the system of families. In order for it to exist, there must be a concept of hatred, for there could be no love without the existence of hatred, as love can be discerned only in contrast to hatred. Without it, there would be no place for families.
Because it is necessary for people to be involved in commerce, there is a need for competitiveness, which is the pillar of commerce. Only in this way does one merchant try to improve on that which another merchant offers, regarding such things as quality of the product, its delivery, etc.
All of these things, though, exist only in this world, where things are considered advantages as if by chance, without intrinsic value. This is because the advantages are just relative to the deficiencies that exist at that time. In contrast, when the world will reach its ideal state of shleimut, it will be a world of good alone. Then all of the contributing factors will also be real ma’a lot (high levels).
The shleimut of humankind is when man perfects his power to choose well to the extent that he is capable of doing. A person should truly desire to see how all of the existence will perfect his power of choice to its fullest. One of the concepts related to the shechina (Divine Presence) is the fulfillment of the Divine desire by means of human choice. There is no way of estimating how great this success will be. For the idea of shleimut through choice is great and wonderful in a way that we will understand only when it will be achieved.
The great spiritual attainment which surpasses the natural world is called an atara (crown). That is why the gemara describes people in the world to come as sitting with crowns on their heads. In other words, they possess that which they acquired through good choices in addition to the personal shleimut that they had naturally. The enjoyment they have is from exposure to the aura of the shechina, in other words, from the pleasantness of realizing the value of fulfilling the Divine desire through human choice. Therefore, the more one is able to succeed as a human to improve and become greater, the greater the pleasantness in the world to come. The significance of the aura of the shechina depends on the level of recognition of the value of the shleimut they achieved through choice. The absolute knowledge of the value is indeed known only to Hashem. However, the level of human understanding increases as a person goes from strength to strength.