This saying of Jesus from Luke’s Gospel is a metaphor for what a disciple is expected to be. It is part of a larger teaching on discipleship.
The context is that of a house at twilight when the lamps are lit to dispel the oncoming darkness. A disciple is like that, a lamp which sheds its light within the house, or at its entrance, inviting outsiders to enter. So must the disciple be, by his gracious words and exemplary behaviour.
God’s word, treasured in the heart of the disciple, makes him or her a beacon to others. A disciple is not meant to be hidden away, “covered under a basin or under the bed”, as if there were something to be ashamed of. Jesus says “rather, let your light shine before all, so that seeing you, men may glorify your heavenly Father.”
Receptivity to God’s word is required of the true disciple. The word of God expands the heart and enriches one’s life, and makes one even more generous, even more blessed. All this is God’s doing. Luke’s final advice: “Take care then, to how you listen.”