God told Abraham to kill his son Isaac because their actions are pointing ahead to the person of Christ in a typology of the true sacrifice. First of all, God says to Abraham to take his only son. But, we know that 13 years earlier Ishmael had been born to Abraham. So why would God call Isaac the only son? The answer becomes clear when we see what the Scriptures teach.
“Now it came about after these things, that God tested Abraham, and said to him, Abraham!’ And he said, ‘Here I am.’ 2 And He said, ‘Take now your son, your only son, whom you love, Isaac, and go to the land of Moriah; and offer him there as a burnt offering on one of the mountains of which I will tell you,’” (Gen. 22:1-2).
When Jesus was having a dialogue with the Jews, they accused him of being demon-possessed. Jesus said, “Your father Abraham rejoiced to see My day, and he saw it and was glad.” 57 The Jews, therefore, said to Him, “You are not yet fifty years old, and have You seen Abraham?” 58 Jesus said to them, ‘Truly, truly, I say to you, before Abraham was born, I am,’” (John 8:56-58). (Note that Jesus claimed divinity by referencing the divine name “I AM.” see Exodus 3:14-15). Now, Jesus said that Abraham saw his day. What did Jesus mean by this? The answer is found in the following chart.
Let’s examine the chart. Both Isaac and Jesus are called the only begotten son. Of course, Abraham knew he had a son named Ishmael. But it was not Ishmael who was the son of the promised covenant; it was Isaac, (Gen. 17:19). That is why God called Isaac Abraham’s only son. Plus, Isaac was representing the future Messiah. Jesus was also called the only begotten son. Also, both Jesus and Isaac were offered on a hill, and most scholars that I have read agree that it was the very same hill upon which they were both offered, though around 1800 years apart.
If you examine the chart, you can see that there is a very close parallel between the sacrifice of Isaac and the sacrifice of Jesus. Furthermore, you should be able to see that Abraham represented God the Father. Isaac represented God the Son. And the servant represented God the Holy Spirit. The sacrifice of Christ was typified in the sacrifice of Isaac.
So, why did Abraham offer his son Isaac? He did so out of obedience – believing that God could raise him from the dead (Heb. 11:19), and also in his obedience, he acted out the true sacrifice of the true only begotten son, Jesus.