John Calvin Commentary Genesis 48:14

"And Israel stretched out his right hand, and laid it upon Ephraim`s head, who was the younger, and his left hand upon Manasseh`s head, guiding his hands wittingly; for Manasseh was the first-born." — Genesis 48:14 (ASV)

And Israel stretched out his right hand. Since his eyes were dim with age, so that he could not, by looking, discern which was the elder, he still intentionally placed his hands across. Therefore, Moses says that he guided his hands wittingly.

He did not rashly extend them, nor transfer them from one youth to the other merely to feel them. Instead, using judgment, he purposely directed his right hand to Ephraim, who was the younger, and placed his left hand on the first-born.

From this we gather that the Holy Spirit was the director of this act. The Spirit illuminated the mind of the holy man, causing him to perceive the nature of this symbolic act more correctly than even the most clear-sighted could. I will avoid saying more on this now, because we will be able to examine it further in other passages.