The binding of Isaac.
No biblical account is so challenging. And none is so crucial.
If Abraham obeys God, the only means for the fulfillment of the covenant will be destroyed. If Abraham does not obey God, there is no covenant.
But the angel of the Lord said to Abraham, “because you have done this and have not withheld your son, your only son, I will surely bless you, and I will surely multiply your offspring as the stars of heaven and as the sand that is on the seashore. And your offspring shall possess the gate of his enemies, and in your offspring shall all the nations of the earth be blessed, because you have obeyed my voice.” Genesis 22:16-18
Read Genesis 16:1-22:19.