Catena Aurea on Luke 2:42–50: A Greek expositor

The feast having been celebrated, while the rest returned, Jesus secretly tarried behind. As it follows, And when they had fulfilled the days, as they returned, the child Jesus tarried behind in Jerusalem; and his parents knew not of it. It is said, When the days were accomplished, because the feast lasted seven days. But the reason of His tarrying behind in secret was, that His parents might not be a hindrance to His carrying on the discussion with the lawyers; or perhaps to avoid appearing to despise his parents by not obeying their commands. He remains therefore secretly, that he might neither be kept away nor be disobedient.