John Calvin Commentary Genesis 20:8

"And Abimelech rose early in the morning, and called all his servants, and told all these things in their ear. And the men were sore afraid." — Genesis 20:8 (ASV)

Therefore Abimelech rose early in the morning. Moses teaches how effective the oracle had been. For Abimelech, alarmed by the voice of God, arose in the morning, not only so that he himself might quickly obey the command given to him, but also so that he might exhort his own people to do the same. An example of such ready obedience is shown to us in a pagan king, so that we may no longer make excuses for our sluggishness, when we benefit so little from divine admonitions.

God appeared to him in a dream; but since he daily cries aloud in our ears—through Moses, through the prophets, and through the apostles, and finally, through his only-begotten Son—it would be absurd to suppose that so many testimonies should have less impact than the vision of a single dream.