The soul can not accomplish its essential mission of purifying the body in the current state of the world. The necessity of death created a reality called the world of souls where the soul would not reach its ultimate completion, but it nevertheless prepares for its return to the body, when it will accomplish its ultimate goal. Derech Hashem 1:3 12

As a result of the sin of Adam, a new interim stage called death was introduced, where the body and soul are separated from their natural state of connection. Derech Hashem 1:3 10-11

In the current state of physical deterioration, after the sin of Adam, the soul does not perform its intended function, which is to purify the body. This is why it is necessary for there to be death, followed by the revival of the dead. This revival will find us in new bodies that are not tainted by Adam's sin, and are therefore capable of being raised by the soul to true spiritual level. Derech Hashem 1:3 9-10

We discuss the concepts of Moshiach ben Yosef and Moshiach ben Dovid, which are intimately intertwined in the current teaching of the Ramchal. Derech Hashem 1:3 6-8

The state of perfect balance between good and evil, the optimal situation for true free choice was Man's state before Adam's sin. Afterwards he fell to a place that needed a new type of rectification before the original state could be attained once again. Derech Hashem 1:3 4-6

We discuss the purpose of creation - Mankind - in his original and natural state. This was a state of perfect balance between good and evil, the optimal situation for true free choice. Derech Hashem 1:3 1-3