***Another way of looking at that is that what the OT God did to Abraham was cruel and sadistic. God would have known Abraham’s faith and that Abraham’s love for God was stronger than for his son. God did not have to test Abraham to know that.
One possibility is that Abraham didn’t know it, and this is how he found out. He obviously grew spiritually as a result of this experience. How many of us can say with absolute certainty what we would do in his sandals then? I believe I have a strong faith, but I can’t say I KNOW what I would do in THAT situation. In addition, God knew that this story would be recorded as a testament to faith for all future believers of all time. This story has certainly helped me with my faith.***
If I may, Abrahams faith was not tested so that GOD would know his faith, but that ABRAHAM would realize it. Testing usually has the effect of causing us to realize where we are strong or weak, something that God already knew.
Do you drastically test your loved ones? Would you load a revolver with blanks, unbeknown to them, and then make them play Russian roulette? If someone did that in real life, he would be locked up and deservingly so for sheer cruelty.