Charles Spurgeon Commentary Genesis 15:4-5

"And, behold, the word of Jehovah came unto him, saying, This man shall not be thine heir; But he that shall come forth out of thine own bowels shall be thine heir. And he brought him forth abroad, and said, Look now toward heaven, and number the stars, if thou be able to number them: and he said unto him, So shall thy seed be." — Genesis 15:4-5 (ASV)

Now was his faith tried indeed. He had no child, he was himself old, and his wife also was old, yet the Lord's promise was, So shall thy seed be as the stars of heaven. Could he believe it? He did.