This article examines Albert the Great's interpretation of John 1:7 concerning John the Baptist: “He came as a witness, to testify about the Light, so that all might believe through him.” Commenting on this verse, Albert develops the idea that the metaphysical approach to God, according to which the notion of God is purified of all sensory images, must be completed by a method that is more connatural to the human being: testimonial knowledge, that is, relying on the senses and imagination, using the metaphors that God himself has suggested through his revelation. Albert's reading of John 1:7 is found to be in continuity with key ideas elsewhere in his oeuvre.