The reason for the resurrection of the body is the final judgement.
Sins are committed while the soul and body are united. So the final judgement happens accordingly.
Romans 7
23 But I see another law in my members, warring against the law of my mind, and bringing me into captivity to the law of sin which is in my members.
24 O wretched man that I am! who shall deliver me from the body of this death?
