This is a very good question for us to consider.  Let’s begin by reading Genesis 22:1-2, “Now it came about after these things, that God tested Abraham, and said to him, “Abraham!” And he said, “Here I am.” Then He said, “Take now your son, your only son, whom you love, Isaac, and go to the land of Moriah, and offer him there as a burnt offering on one of the mountains of which I will tell you.”” (NASB).  What an incredible test…to be told to offer your son as a burnt offering to the Lord!  How did Abraham respond to such a test?  We read in verse 3, “And Abraham ROSE UP EARLY IN THE MORNING, and saddled his ass, and took two of his young men with him, and Isaac his son, and clave the wood for the burnt offering, and rose up, and went unto the place of which God had told him.”  Immediate and unwavering obedience!  Abraham did not question the Lord or argue with Him…he simply obeyed. 

What thoughts must have entered Abraham’s mind!  He surely must have remembered how the Lord told him that it would be through Isaac that his heritage would be established.  We read in Genesis 21:12, “And God said unto Abraham…in Isaac shall thy seed be called.”  How could God give Abraham seed through Isaac if he was to be sacrificed to God?  We get a glimpse into Abraham’s mind at this time by reading Hebrews 11:17-19, “By faith Abraham, when he was tried, offered up Isaac: and he that had received the promises offered up his only begotten son, Of whom it was said, That in Isaac shall thy seed be called: ACCOUNTING THAT GOD WAS ABLE TO RAISE HIM UP, EVEN FROM THE DEAD; from whence also he received him in a figure.”  Abraham fully intended to offer Isaac as a burnt offering to God, believing that God would raise Isaac back to life.  So, he went forth determined to fully comply with God’s command.  This is shown in Abraham’s words to his servants in Genesis 22:5, “…Abide ye here with the ass; and I and the lad will go yonder and worship, AND COME AGAIN TO YOU.”  Our dear patriarch fully expected to bring Isaac back with him from the mountain…after the Lord raised him from the dead. 

I encourage you to read this event in Genesis 22:1-10 to see how Abraham was faithful and Isaac was willing to do the Lord’s will that day.  As Abraham raised his knife above his head to slay his son, we read in verses 11-12, “And the angel of the LORD called unto him out of heaven, and said, Abraham, Abraham: and he said, Here am I. And he said, Lay not thine hand upon the lad, neither do thou any thing unto him: for NOW I KNOW that thou fearest God, seeing thou hast not withheld thy son, thine only son from me.”  As you asked, did God not fully know what Abraham would do?  Yes, He most certainly did.  It is not that God learned anything about Abraham’s obedience and faithfulness that He did not previously know; but these qualities had now been made apparent.  They had been manifested by outward acts.  Indeed, God knew from past eternity what Abraham would do.  This may be understood as a knowledge of approbation, that the Lord now experienced, and approved of the faith, fear, love, and obedience of Abraham.

Although the Lord knew exactly what his servant would do, perhaps Abraham needed to have his faith tested so that he could be assured of God’s working in his heart.  Through this test, Abraham learned more about his own heart towards the Lord. 

In Psalm 139:1, David said, “O LORD, thou hast searched me, and known me.”  He understood God’s complete knowledge of himself; indeed God knew David better than David knew himself.  David ended this psalm with a request of the Lord, “Search me, O God, and know my heart: try me, and know my thoughts: And see if there be any wicked way in me, and lead me in the way everlasting.” (Verses 23-24).  God had searched David’s heart and knew all about him.  David’s desire was that the Lord would search his heart and reveal its contents to him, so that he might identify and rid himself of any wickedness in himself and be led in the way everlasting.  Dear friend, may that be our prayer, too.  Let us look to the Lord to show us what we cannot see on our own…the contents of our own heart.  May we invite Him to expose any evil thoughts or desires that might lurk there, so that we might confess these things and commit our hearts and lives to the Lord…and walk (live) according to His way which is always perfect.  (CC)  (708.2)