Read: Genesis 21 and 22
I will bless her, and moreover, I will give you a son by her. I will bless her, and she shall become nations; kings of peoples shall come from her. But I will establish my covenant with Isaac, whom Sarah shall bear to you at this time next year. The Lord visited Sarah as he had said, and The Lord did to Sarah as he had promised. (Genesis 17:16, 21; 21:1 ESV)
He said, Take 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. 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. So they went both of them together. And the angel of the Lord called to Abraham a second time from heaven and said, By myself I have sworn, declares the Lord , because you have done this and have not withheld your son, your only son, I will surely bless you, and I will surely multiply your offspring as the stars of heaven and as the sand that is on the seashore. And your offspring shall possess the gate of his enemies, and in your offspring shall all the nations of the earth be blessed, because you have obeyed my voice. (Genesis 22:2, 7, 8, 15-18 ESV)
God demonstrated his love for Abraham by promising him a son; but then—in what seems to be a strange twist—God asks Abraham to take his son to a mountaintop and sacrifice him. Abraham was an old man by the time Isaac was born. His wife Sarah had already passed her natural season for child birth. Abraham follows the heart of God in faith. Isaac himself willingly complies with the will of his father.
All of this points ahead to Jesus. God, loved his creation so much that He sent a promised son, His only begotten son. The Son of God, Jesus Christ, willingly complied with the Father. Whereas Isaac was spared upon the mountain by divine intervention, Jesus was not. Instead Jesus became our divine intervention to spare us from the fate of eternal damnation.
Sometimes it is hard to hold on to the promises we feel that God has put in our heart. God knows us better than we know ourselves. He knows our flaws, frustrations, and failures. He himself intervened for us for a promised deliverance. Whatever you feel God has promised you in your heart, hold on to it. Hold true to it. Do not waiver. Show the faith of Abraham and Isaac. Jesus is worth it.