Is the incarnation of Jesus permanent, according to reformers like Luther or Calvin?

Question

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".

My question:
Is there any reading about this matter from Luther or Calvin or any other Reformed Church's father?

Answer 1

The idea of permanent incarnation has been most famously expressed in the Council of Chalcedon, long before the Reformation – there Christ's natures are said to exist "indivisibly, inseperably."

Reformers like Luther and Calvin upheld the Chalcedonian definition, and this can be seen in their writings. For example, here's a brief quote from Calvin:

While our whole Mediator is everywhere, he is always present with his people, and in the Supper exhibits his presence in a special manner; yet so, that while he is wholly present, not everything which is in him [i.e., spirit and body] is present, because, as has been said, in his flesh he will remain in heaven till he come to judgment. (Calvin's Institutes, IV.18.30)

In context, Calvin clearly holds that Christ continues to have both a spirit and a body, and that his body is in heaven, while is spirit is everywhere.

Here are two more quotes that come from a foundational document of one branch of the Reformation, the Westminster Confession of Faith:

So that two whole, perfect, and distinct natures, the Godhead and the manhood, were inseparably joined together in one person (Westminster Confession of Faith 8.2)

On the third day He arose from the dead, with the same body in which He suffered, with which also he ascended into heaven, and there sits at the right hand of His Father (WCF 8.4)

So yes, leading reformers held that Christ still has two natures, both human and divine.

Answer 2

The permanent and eternal union of Divine nature and human nature in Jesus Christ is clearly stated by Martin Luther (in XXX111 articles) in his 'disputation' :

On the Divinity and Humanity of Christ

Wikipedia

I would not wish to merely transpose text en masse from that document as I think it speaks for itself.

But in answer to the comment, I would quote Luther's article IX :

The humanity joined with the divinity is worshipped; the humanity of Christ is worshipped, and not falsely, for it is inseparable from the divinity