thanks for the question. We'll dive right in...
"We know the LORD knows everything, past, present and future. Right? "
Yep, right. The Bible is clear on that.
1Jn 3:20 whenever our hearts condemn us. For God is greater than our hearts, and he knows everything.
Isa 46:9-10 Remember the former things, those of long ago; I am God, and there is no other; I am God, and there is none like me. (10) I make known the end from the beginning, from ancient times, what is still to come. I say: My purpose will stand, and I will do all that I please.
Psa 139:4 Even before there is a word on my tongue, Behold, O LORD, You know it all.
So why then test Abraham when God already knew what he would do? There will be more things that I haven't thought of for sure, but here are some quick points to consider.
- The test is not for God but for Abraham to know his own heart
The tests we go through, whether it is Abraham 4000 years ago or our own tests today are not for God to know our hearts but so that we see our hearts. While we talk about faith, surrender and obedience, all of this is actually proved in the difficult trials... not while the sun is out and the birds are chirping so to speak! This was a huge test for God to ask Abraham to go through but he did so in faith. Abraham would have learnt about trusting God in the really difficult times and so do we in our tests. Hebrews 11 tells us that:
Heb 11:17-19 By faith Abraham, when God tested him, offered Isaac as a sacrifice. He who had received the promises was about to sacrifice his one and only son, (18) even though God had said to him, "It is through Isaac that your offspring will be reckoned." (19) Abraham reasoned that God could raise the dead, and figuratively speaking, he did receive Isaac back from death.
- The test is because Heaven is watching!
While God knows all things, the angelic beings, both good and bad, don't. They are all involved in what plays out on this earth behind the scenes and watch to see what will happen in various situations. They are still learning about the wonders of this limitless God and marvel at His ways. See Eph 3:10-11. So they would have been watching this dramatic event with Abraham. Here was Abraham whom they knew God had chosen to be the Father of the chosen race. He had waited so long for the promised son. And now he was asked to sacrifice him? Would he pass this test? Would he trust God and be obedient even when many of the angels themselves hadn't? Satan and the fallen angels would have been looking for, and working towards, Abraham failing. How would it play out? The unseen realm was watching!
- The test is so Abraham can be rewarded justly and be seen to rewarded justly.
There is perfect justice in all that God does. And He often demonstrates that justice. He could have just rewarded and blessed Abraham greatly without any tests (just based on what He knew Abraham would do if tested) but that wouldn't be seen to be just. In allowing this test to play out, all the heavenly realm, and all those that would come afterwards (including you and me), can look on and see God is justified in His actions of rewarding Abraham and blessing him richly for Abraham walked in faith and obedience - even in very difficult circumstances! Jer 17:10 I the LORD search the heart and examine the mind, to reward a man according to his conduct, according to what his deeds deserve.
This was what the angel of the Lord said to Abraham once it was seen that he was obedient to God's call to offer up Isaac.
Gen 22:15-18 The angel of the LORD called to Abraham from heaven a second time (16) and said, "I swear by myself, declares the LORD, that because you have done this and have not withheld your son, your only son, (17) I will surely bless you and make your descendants as numerous as the stars in the sky and as the sand on the seashore. Your descendants will take possession of the cities of their enemies, (18) and through your offspring all nations on earth will be blessed, because you have obeyed me."
- The test is so Abraham can enter into a part of what God Himself would experience
This is an interesting one. Abraham would be the father of many nations but the father of God's chosen nation, the Jewish nation, especially. As the father, God allowed Abraham to experience a little of what He Himself, as the Heavenly Father, would experience in offering up His only Son - Jesus. There will be a depth here we know little about.
- The test is so all of us could see the plan of God in 2000 years in advance
God likes to show what He is going to do in advance. Especially when it comes to the greatest event in human history - the death and resurrection of His Son! Sometimes this is through prophecies, sometimes through outward pictures that are played out in peoples lives. He did that with all the Jewish feasts and sacrifices and He definitely did it here with Abraham and his son Isaac. It is a picture, 2000 years in advance, of what the Father would do with Jesus. I've written elsewhere abut this several times. It is an amazing picture, with God even taking Abraham to the exact same spot as where the Jewish temple and it's sacrifices would be! (2 Chr 3:1)
- The test is so we also could learn and follow Abraham's example
All the tests Abraham went through teach us as well. Speaking of Abraham's testing time in waiting for the promised Son (even when all hope seemed lost from a natural point of view) we read:
Rom 4:20-24 Yet he did not waver through unbelief regarding the promise of God, but was strengthened in his faith and gave glory to God, (21) being fully persuaded that God had power to do what he had promised. (22) This is why "it was credited to him as righteousness." (23) The words "it was credited to him" were written not for him alone, (24) but also for us, to whom God will credit righteousness--for us who believe in him who raised Jesus our Lord from the dead.
Looking at Abraham's test of offering up Isaac, this was a test my brother in law and sister had to face with their first-born son Jason. It's a long story but he nearly died (he was born with hydrocephalus and had had numerous operations on his brain over many years) and, though they tried, there was basically nothing the doctors could do. It particularly came to a climax when Jason was about 8. There were countless emergency trips to the hospital. Everyone was praying etc but nothing was going well. The doctors had fairly much given up saying there was nothing they could do. At that point, when all natural hope was gone, Jason's dad knew God wanted him to hand his son over - whether that be for life or death. So He said to God something to the effect of 'Jason is your son, not mine, and if it is time to take him home, your will be done!' I can't do it justice in a few words because it was quite amazing and it was a long dramatic time getting to that point of absolute surrender... but that is what my bro-in-law did and his son Jason not only got better from that point, but he is now married with a child of his own and has never required another operation since that day. It really was a miracle... and our family always call it our Abraham experience. Now God doesn't require such dramatic things to happen with all obviously. But we can all learn from Abraham's faith in some way because we all have things that we will need to let go of and place in the hands of God, trusting Him - no matter what the outcome.
Hope that helps. Like I said there will be other things but it gives some thoughts on why God tested Abraham like He did.