God told Abraham that he would be the Father of many nations, and that through his seed all the families of the earth would be blessed. This is certainly true, even though it seemed to be impossible at the time.
God told Abraham to offer Issac as a sacrifice. Even though this defied logic, Abraham was willing to do it anyway. He trusted that God would do them no harm, and that he would fulfill his promise.
He didn’t know what God had in mind. We know that he expected God to raise Issac from the dead. If you read this whole story in Genesis 22, you’ll see that Abraham told his servants to wait and that, “I and the lad . . will come again to you.”
Abraham knew God and his ways very well. He had based his whole life on believing God’s word. This is what the Bible says about him:
He staggered not at the promise of God through unbelief; but was rich in faith, giving glory to God; And being fully persuaded that, what he had promised, he was able also to perform. And therefore it was imputed to him for righteousness.
Now it was not written for his sake alone, that it was imputed to him; But for us also, to whom it shall be imputed, if we believe on him that raised up Jesus our Lord from the dead; (Romans 4:20-24)
What exactly did Abraham do that was so remarkable. He believed God to the extreme extent of being willing to obey him. All he provided was the willingness. God provided everything else, including the sacrifice–one for Issac and one for us.
God even provides us the faith we need to believe his word. As it is written, So then faith cometh by hearing, and hearing by the word of God. (Romans 10:17)