the promise still remains
And behold, the word of the Lord came to [Abraham], saying, “This one shall not be your heir, but one who will come from your own body shall be your heir.” [Genesis 15:4]
Then He said, “Take now your son, your only son Isaac, whom you love, and go to the land of Moriah, and offer him there as a burnt offering on one of the mountains of which I shall tell you.” So Abraham rose early in the morning and saddled his donkey, and took two of his young men with him, and Isaac his son; and he split the wood for the burnt offering, and arose and went to the place of which God had told him. Then on the third day Abraham lifted his eyes and saw the place afar off. And Abraham said to his young men, “Stay here with the donkey; the lad and I will go yonder and worship, and we will come back to you.” [Genesis 22:2-5] (emphasis added)
Abraham was asked to do what seemed so contrary to the plan that God had revealed to him, but it was only a test of his faith. We need faith in God, that what He has set in motion in our lives He will finish. Abraham knew he was coming back with his son, and we need to have the same constant faith in God’s plan for our own lives.