Two natures of Christ
In order for my salvation to be sure and complete, I know that God himself had to die. A man alone dying would not save me. I thought that I had been taught that since Christ's human nature shares with his divine, and his divine nature with his human, that both natures of Christ died on the cross. Recently I was corrected by another WELS member telling me that only the human nature actually died, because "God cannot die." Would you please help clarify. Which Bible verses speak to this? Thank you for your help.
You are correct in noting that, in order for our salvation to be “sure and complete,” Jesus had to be more than a man when he offered his life on the cross. Scripture says “No man can redeem the life of another or give to God a ransom for him—the ransom for a life is costly, no payment is ever enough” (Psalm 49:7-8).
Jesus is the God-Man. The angel Gabriel informed Mary that the child she would give birth to would be called “The Son of the Most High” (Luke 1:32) and “the Son of God” (Luke 1:35). God and man in one person is a “mystery” (1 Timothy 3:16) to us, but we cling to that mystery in Spirit-worked faith.
You also understand correctly that there is a union of the two natures in Christ, and so it is accurate to speak of God dying on the cross. In fact, church history is replete with individuals who denied that and whose errors led the Christian church to formulate responses from Scripture.
In Acts 20:28 the apostle Paul instructed the elders of the church in Ephesus to “Be shepherds of the church of God, which he bought with his own blood.” It was not the shed blood of a mere man that ransomed people, it was God’s “own blood.” Similarly, in 1 John 1:7 the inspired writer comforts us with the message that “the blood of Jesus, his Son, purifies us from all sin.” Again, it is not the blood of a mere man that cleanses us from all sin, but the blood of God’s Son.
Just an aside—it is Scripture alone that is the foundation of our faith, but it is interesting to see how our hymns reflect the truths of our faith. In that regard, take a look at some of the hymns in the Lent and Good Friday section of Christian Worship. Several hymns illustrate the truth of Scripture that God died in our behalf, to win our salvation. The refrain of one such hymn points us to a God-pleasing response: “Thousand, thousand thanks shall be, Dearest Jesus, unto thee.” (Christian Worship 114)