Abraham said, "God will provide for himself the lamb for a burnt offering, my son." (Genesis 22:8, ESV).

God will provide -- this is what Abraham believed.

In faith, he had taken his son, Isaac, up to the mountain that God showed him so that Isaac would be sacrificed unto God. Abraham believed God would raise Isaac from the dead. Since God had promised Isaac was the promised seed, and he'd not yet had a child of his own, Abraham believed God had to raise Isaac back to life (Hebrews 11:19). Abraham was living according to the Word and promise of God.

The passage was not designed to promote child sacrifice. Instead, it shows us the depravity and disgusting nature of it so that we might appreciate the cross of Jesus Christ, the Son of God, who allowed himself to be sacrificed for us.

But on the way up to that mountaintop, Isaac said to his father, "Where is the sacrifice?" Abraham, "God will provide for Himself the lamb for a burnt offering. God will provide."

Now, ultimately, Abraham's promise was fulfilled in Jesus. God provided the ultimate Lamb, Jesus.

But here's Paul's argument in Romans:

What then shall we say to these things? If God is for us, who can be against us? He who did not spare his own Son but gave him up for us all, how will he not also with him graciously give us all things? (Romans 8:31–32, ESV).

If God provided the Lamb, his only begotten Son, will he then not freely give to his people all they need? God provided himself. So, as Abraham said, God will provide.