2 Corinthians 4:6 For it is the God who commanded light to shine out of darkness, who has shone in our hearts to give the light of the knowledge of the glory of God in the face of Jesus Christ.
In order for a torch to be able to shine in the darkness it must have a source of energy that will allow the light to shine bright. Nowadays that is a case of putting a battery into the torch and switching it on!
But for us to be able to shine for others we need a source of energy that others do not have. That source then needs to feed the light that will shine forth.
That source is the Word of God. That light is our lives. Christ has given us the knowledge so that we can use that source to shine brightly in the world so others can find out that knowledge too.