Yet (Romans 4 verse 18) “against all hope, Abraham in hope believed and so became the father of many nations, just as it had been said to him,
“So shall your offspring be". Without weakening in his faith, he faced the fact that his body was as good as dead - and that Sarah’s womb was also dead.
Abraham trusts God that even through death God will keep His promise.
Yet even as his heart pains within him, he knows he must bring Isaac as a burnt offering, before God.
Hebrews 11 verse 17 to19:
By faith Abraham, when God tested him, offered Isaac as a sacrifice. He who had embraced the promises was about to sacrifice his one and only son, even though God had said to him: “It is through Isaac that your offspring will be reckoned. Abraham reasoned that God could even raise the dead, and so in a manner of speaking he did receive Isaac back from death.
This story is very similar to the story of the birth, suffering and sacrifice of Gods only-begotten Son; Jesus Christ.
Abraham has seen this by faith: John 8 verse 56:
your father Abraham rejoiced at the thought of seeing my day; he saw it and was glad.
When Ishmael and his mother Hagar have been driven away, Isaac grows up as heir of Abraham and Sarah. Abraham’s faith is tested by the command of God to offer Isaac as a burnt offering. Waiting for a son to be born had been quite a test.