God can't die, but Jesus died, so how can he be God?

This a common assertion, however the truth is that within the one person, Jesus Christ, is the human nature and the divine nature (hypostatic union). Jesus’ human nature could die, but his divine nature couldn’t and didn’t die.

Christ is God incarnate, that is, God in the flesh. As the book of John says, "In the beginning was the Word, and the Word was with God, and the Word was God … And the Word became flesh and dwelt among us, and we have seen his glory, glory as of the only Son from the Father, full of grace and truth" (John 1:1, 14). Jesus is both God and man. Jesus Christ died on the cross, but in saying that we aren’t saying his divine nature died. Jesus died as a man to redeem mankind. Man has no divine nature, so there was no reason why the divine nature of Christ needed to die. Moreover, Jesus didn't sin (he couldn't because of his divine nature), so he needed no atoning.

A couple of heresies arose in the early church regarding this issue — theopassianism and patripassianism. Theopassianism teaches that God himself suffered death on the cross, and patripassianism teaches that the God the Father suffered vicariously through the suffering of God the Son. Both of these heresies deny the unchanging character and nature of God, that is, his immutability (cf. Mal. 3:6; Jas. 1:17). The substantive nature of God can’t change! The divine nature isn’t capable of experiencing and suffering death. Death is something that may only be experienced by the human nature. [1]

Charles Spurgeon masterfully sums it up:

I shall offer some exposition of my text [Mal.3:6], by first saying, that God is Jehovah, and he changes not in his essence. We cannot tell you what Godhead is. We do not know what substance that is which we call God. It is an existence, it is a being; but what that is, we know not. However, whatever it is, we call it his essence, and that essence never changes.

The substance of mortal things is ever changing. The mountains with their snow-white crowns, doff their old diadems in summer, in rivers trickling down their sides, while the storm cloud gives them another coronation; the ocean, with its mighty floods, loses its water when the sunbeams kiss the waves, and snatch them in mists to heaven; even the sun himself requires fresh fuel from the hand of the Infinite Almighty, to replenish his ever-burning furnace. All creatures change. Man, especially as to his body, is always undergoing revolution. Very probably there is not a single particle in my body which was in it a few years ago. This frame has been worn away by activity, its atoms have been removed by friction, fresh particles of matter have in the meantime constantly accrued to my body, and so it has been replenished; but its substance is altered.

The fabric of which this world is made is ever passing away; like a stream of water, drops are running away and others are following after, keeping the river still full, but always changing in its elements. But God is perpetually the same. He is not composed of any substance or material, but is spirit-pure, essential, and ethereal spirit-and therefore he is immutable. He remains everlastingly the same. There are no furrows on his eternal brow. No age hath palsied him; no years have marked him with the mementoes of their flight; he sees ages pass, but with him it is ever now. He is the great I AM-the Great Unchangeable.

Mark you, his essence did not undergo a change when it became united with the manhood. When Christ in past years did gird himself with mortal clay, the essence of his divinity was not changed; flesh did not become God, nor did God become flesh by a real actual change of nature; the two were united in hypostatical union, but the Godhead was still the same. It was the same when he was a babe in the manager, as it was when he stretched the curtains of heaven; it was the same God that hung upon the cross, and whose blood flowed down in a purple river, the self-same God that holds the world upon his everlasting shoulders, and bears in his hands the keys of death and hell. He never has been changed in his essence, not even by his incarnation; he remains everlastingly, eternally, the one unchanging God, the Father of lights, with whom there is no variableness, neither the shadow of a change.

God not only created the universe, He sustains it by the very power of His being. As Paul said, "In Him we live and move and have our being" (Acts 17:28). If the being of God ceased for one second, the universe would disappear. It would pass out of existence, because nothing can exist apart from the sustaining power of God. If God dies, everything dies with Him. Obviously, then, God could not have perished on the cross. [2]

Footnote

[1] Death may be experienced by animals, plants, etc. but that type of death isn’t being discussed here.
[2] Spurgeon, C.H. A Sermon on Malachi 3:6 (No. 1). Delivered on Sabbath Morning, January 7th, 1855, at New Park Street Chapel, Southwark.

Related Topics

How can Jesus make intercession to Father, if he and the Father are one God?