John Calvin Commentary Genesis 37:30

"And he returned unto his brethren, and said, The child is not; and I, whither shall I go?" — Genesis 37:30 (ASV)

And he returned. We may from this gather that Reuben, under the pretext of some other business, secretly left his brothers. His intention was, without their knowledge, to restore his brother to their father after taking him out of the pit. Therefore, he was absent when Joseph was sold.

It is no wonder that he was forestalled, since he had gone a different way than they did, intending to reach the pit by a roundabout path.

But now, at last, Reuben, having lost all hope, reveals to his brothers the plan he previously did not dare to confess, for fear that the boy would be immediately murdered.