Simple. I’m just glad that your friend asked you. As a Christian, perhaps your friend has not yet been educated in the basics of the history of Christianity which, of course, began with the Hebrews (God’s chosen people).
This is to be considered in the entire context of sacrifice…
The passover of the Angel of Death over the lentils of the Chosen People who obeyed by slaying a lamb and putting the blood of the lamb over the lentils of their doors so that the Angel of Death would not kill the first born of that household was a pre-cursor in the Hebrew Scriptures (what we Christians sometimes call “the Old Testament”) of the sacrifice of the Son of God (Son of Man) Jesus the Christ to save us all… not just those who believe in Him.
beginning with Abraham obeying God by putting his own son on the stone to kill him as a sacrifice to God in a way that people killed lambs… and God – seeing that Abraham was SO willing to obey Him that He told Abraham that He was not going to require that Abraham shed his son’s blood after all because of Abraham’s faith is what saved his son.
God, being All-Knowing (among other “All-” things), absolutely already knew/knows about anybody’s faith. After all, He’s the one who gives it freely as a gift to everybody.
God wants us to acknowledge our Faith. Even “today” those of us who are living in an era of the world that is after Jesus’ redemption of us all – God wants us to tell Him that we believe.
It’s NOT for GOD’s benefit that we do so. It’s for OUR OWN.
Hope this helps your friend to understand something that can’t really be covered in its entirety on a TV show or movie.