Abraham's offering of Isaac

Finally, God gave Sarah the promised son, Isaac. Due to her love of Isaac and her jealousy of Hagar and Ishmael she expelled the two. Abraham was loathe to abandon Ishmael to the elements, but God promised to take care of Ishmael, and that he would be the father of of a nation, so Abraham trusted God and did what he was told. 

But God wasn't done testing Abraham. He asked Abraham to bring Isaac up the mountain and sacrifice him. Abraham did so, but just as he was about to kill Isaac, an angel called called to him from heaven, telling him not to sacrifice Isaac, but to sacrifice a lamb that was caught in the brambles. 

This is another example of why I wonder if God was considered omnipotent by the writers of the Pentateuch. I wonder why God did so much testing of Abraham if God knew that Abraham would pass. It seems cruel. 

I was disappointed in the Abraham's personality again when he lied to Isaac about the sacrifice: "And Isaac said to his father Abraham, 'My father!' And he said, 'Here am I, my son.' He said, 'Behold, the fire and the wood, but where is the lamb for a burnt offering?' Abraham said, 'God will provide for himself the lamb for a burnt offering, my son.'" (Genesis 22:7-8 ESV) Wouldn't it have been better for Abraham to give Isaac the chance to volunteer for the mission? God did not order Abraham to lie to his child.