Before, I thought that by the time Jesus died, that's the end of His incarnation state after He fulfilled His role, spilling His blood for the forgiveness of sins.
Below is an article I found in this link about the purpose of the Incarnation :
Second, it was necessary for the Savior to shed His blood for the forgiveness of sins (Hebrews 9:22). A blood sacrifice, of course, requires a body of flesh and blood.
So... from the article above (my own conclusion) :after the purpose of the Incarnation achieved – God return to His original/default state which is a spirit (without flesh) and has one nature only. This state doesn't mean that God cannot "flesh" Himself anymore.
But I just know it today from the internet that God incarnation is permanent. Just like if today there is someone say, then he say : "God in heaven now is not just a spirit but a spirit with a human flesh - God now is not only with one nature but two natures".
Is there any reading about this matter from Luther or Calvin or any other Reformed Church's father?