It is probable that by this time, Isaac had learnt that the thing was of God. He now speaks positively that the blessing is sure.
Genesis 27:29-33
29 Let people serve thee, and nations bow down to thee: be lord over thy brethren, and let thy mother's sons bow down to thee: cursed be every one that curseth thee, and blessed be he that blesseth thee.
30 And it came to pass, as soon as Isaac had made an end of blessing Jacob, and Jacob was yet scarce gone out from the presence of Isaac his father, that Esau his brother came in from his hunting.
31 And he also had made savoury meat, and brought it unto his father, and said unto his father, Let my father arise, and eat of his son's venison, that thy soul may bless me.
32 And Isaac his father said unto him, Who art thou? And he said, I am thy son, thy firstborn Esau.
33 And Isaac trembledd very exceedingly, and said, Who? where is he that hath taken venison, and brought it me, and I have eaten of all before thou camest, and have blessed him? yea, and he shall be blessed.