Genesis 15:5
And he brought him forth abroad, and said, Look now toward heaven, and tell the stars, if thou be able to number them: and he said unto him, So shall thy seed be. And he brought him forth abroad, and said, Look now toward heaven, and tell the stars, if thou be able to number them: and he said unto him, So shall thy seed be.
God led Abraham outside under the night sky and invited him to count the stars if he could, promising that his descendants would be just as countless. Though he was childless and thought his trusted servant might be his heir, he was assured that his heir would be his own son, with the promised line to run through Isaac and not through Ishmael. Abraham believed the promise, and his faith was counted to him for righteousness. The long delay tested that faith and led to the wrong step of taking Hagar, and nearly fifty years later the command to offer Isaac seemed to destroy the promise, yet Abraham obeyed in trust that God could raise Isaac from the dead. The pledge of a seed numberless as the stars pointed forward to the coming of the Messiah, and its slow fulfillment let the chosen people increase apart in Egypt until the appointed time.
Promise of Countless Descendants
God brought Abraham forth abroad under the night sky and bade him look toward heaven and tell the stars, if he were able to number them, declaring that so should his seed be, too numerous to count. The sign was the stars themselves, set before his eyes as the measure of a posterity beyond human counting. That assurance was given while the fulfillment still lay wholly in the future and rested on God himself to accomplish.
Abraham at that time had no son and thought his trusted servant Eliezer might become his heir, but God ruled out Eliezer and assured him his heir would be his own real son. Abraham believed God, and his faith was counted to him for righteousness. The promise of a seed numberless as the stars was a prophecy of the Messiah's coming, which gave hope as John studied the prophetic revelations of Christ.
Faith Tested and Fulfilled
The line promised to become countless as the stars was to continue through Isaac, not through Ishmael. The long delay before a son was born tested Abraham's faith in God's power and timing. Abraham accepted the promise, yet he failed to wait for God to fulfill it in His own way. Sarah, thinking a child could not be born to her in her old age, proposed Hagar as a means of fulfilling God's purpose, and the failure to wait in faith for the promised son brought unhappiness.
Nearly fifty years afterward Abraham recalled the promise of descendants too numerous to count like the stars when God commanded him to offer Isaac, the son through whom it was to be fulfilled. The command seemed to threaten the promised future, and he wondered how it could be fulfilled through Isaac if Isaac were put to death. Yet he trusted God and obeyed, hoping that God could raise Isaac from the dead.
The promise had not yet been fulfilled because the chosen people had increased only slowly. Canaan could not then support their rapid growth without their displacing its inhabitants before the appointed time or risking idolatry through contact with them. Egypt offered fertile land for their increase, while Egyptian antipathy toward shepherds helped keep them separate, so their growth in Egypt served the fulfillment of the promise.