Charles Spurgeon Commentary Genesis 22:6

"And Abraham took the wood of the burnt-offering, and laid it upon Isaac his son. And he took in his hand the fire and the knife. And they went both of them together." — Genesis 22:6 (ASV)

And Abraham took the wood of the burnt offering, and laid it upon Isaac his son; and he took the fire in his hand, and a knife;

That knife was cutting into his own heart all the while, yet he took it. Unbelief would have left the knife at home, but genuine faith takes it.