This famous quote comes from Act V, Scene 2 of Shakespeare's Othello. The line is spoken by Othello as he enters his wife Desdemona's bed chamber, intending to murder her for suspected infidelity. The line refers both to the putting out of a candle, and to the ending of Desdemona's life. Here, Lestat appropriately quotes it as he knocks over a candle, extinguishing the flame, and prepares to murder a woman in his hotel room.
Put out the light, and then put out the light:
If I quench thee, thou flaming minister,
I can again thy former light restore