Gan Eden is only for the soul and the resurrection is for the body and the soul.
A. Our sages give the following example:
The owner of an orchard hired a blind man and a crippled man to guard the orchard. One day the blind man turns to his friend and says “I have an idea how we can steal fruit from the orchard. You climb onto my shoulders and tell me where to go and you will be able to pick the fruit and share them with me!”
When the owner came to the field and noticed the missing fruit he questioned them about it.
“How could I have stole the fruit, I can’t even walk” said the handicapped guard.
And the blind person insisted that he could not have stolen because he could not see.
The owner, who quickly grasped what had happened, put the blind person atop his crippled friend and punished them together.
So too when the Day of Judgment arrives, both the soul and the body claim to be innocent. The body protests that it is merely a sack of flesh and bones without the soul, but the soul argues that it is the evil bodily desires that caused him to sin.
It is therefore only right that both the body and the soul share any reward or punishment that they earned.
B. According to chassidic teachings, G-d desired to have a dwelling place here in this physical world.
We were created to transform this mundane world into a divine dwelling place for G-d. This is accomplished through our doing mitzvos, because every mitzvah that we do suffuses the physical object with which the mitzvah is performed with holiness and G-dliness. When the world has been saturated with enough mitzvos and holiness Moshiach will come and all the G-dliness which we brought into the world throughout the generations will be revealed.
It is therefore necessary for the physical body to be resurrected to witness the revelation of G-d in this physical world.
This article is reprinted from AskMoses.com