Why was that necessary if he had already been declared righteous? (Gen 15:6, as you pointed out)
Abraham received a saving act of grace by God and was faithful thereafter
And he was already known to be faithful extending to his family? i.e., it didn't appear to be because of the interrupted sacrifice of Isaac that Abraham was faithful thereafter.
Genesis 18:19 KJV — For I know him, that he will command his children and his household after him, and they shall keep the way of the LORD, to do justice and judgment; that the LORD may bring upon Abraham that which he hath spoken of him.
verse showing God's foreknowledge
Genesis 18:19 KJV —
So if there's no gain for eather God or Abraham, why go through it at all?
Abraham received a saving act of grace by God and was faithful thereafter
Rather it was part of a process of God testing Abraham, first to leave his homeland, then to trust for a new home, then to trust for a child-heir (from Sarah), then to trust for God's provision no matter what (he was confident that God could raise him from the dead, even:
Hebrews 11:19 KJV — Accounting that God was able to raise him up, even from the dead; from whence also he received him in a figure.
But not at first. Abraham was not that trusting at first. He didn't think God could give him a child by Sarah. So the testing came over 25 years until Isaac was born, then another bunch of years (unspecified, but I'd propose 15) until the almost sacrifice.
so not testing God
we the readers have God prophesying his own sacrifice for the sin of the world scape goat and all.
(Romans 4:16) Therefore it is of faith, that it might be by grace; to the end the promise might be sure to all the seed; not to that only which is of the law, but to that also which is of the faith of Abraham; who is the father of us all,
Did God do this for Abraham's gain or God's? Why not both? Abraham grew in knowledge of God, why can't God grow in knowledge of Abraham? Isn't it only because you have already decided that God already knows all future things based on other verses that don't require it?
Abraham grew in faith , God already knew ,Genesis 18:19
(Job 21:22) Shall any teach God knowledge, since He shall judge the exalted?
(Romans 11:34) For who hath known the mind of the Lord? or who hath been his counsellor?
