The parable begins with the fact that no one hides a light they have prepared. Thus, the light or truth from God will not be hidden. Next, he says everything hidden will be revealed, i.e., God’s light will reveal everything.

Thus, the truth and the error are there to be known. So, he says be careful as to what you choose to hear. If you are attentive, your ability to grasp truth will increase. If not, you will become duller as to spiritual truth.