What a disturbing thought. It is possible that a person's "light" is actually darkness; a person's "truth" is actually a lie; a person's "knowledge" is actually error; a person's "wisdom" is actually foolishness. Jesus said, "Take heed therefore that the light which is in thee be not darkness."
Luke 11:35
(35) Take heed therefore that the light which is in thee be not darkness.
The light of God is given to those who walk in the light, those who trust and obey God, those who abide in Christ. The HOLY Spirit bears witness to the truth. If it does not promote holiness of heart and life, it is not of God.
1 John 3:24-4:6
(especially vss. 3:24, 4:1, 4, 5, 6)
(3:24) And he that keepeth his commandments dwelleth in him, and he in him. And hereby we know that he abideth in us, by the Spirit which he hath given us.
(4:1) Beloved, believe not every spirit, but try the spirits whether they are of God: because many false prophets are gone out into the world.
(4:2) Hereby know ye the Spirit of God: Every spirit that confesseth that Jesus Christ is come in the flesh is of God:
(4:3) And every spirit that confesseth not that Jesus Christ is come in the flesh is not of God: and this is that spirit of antichrist, whereof ye have heard that it should come; and even now already is it in the world.
(4:4) Ye are of God, little children, and have overcome them: because greater is he that is in you, than he that is in the world.
(4:5) They are of the world: therefore speak they of the world, and the world heareth them.
(4:6) We are of God: he that knoweth God heareth us; he that is not of God heareth not us. Hereby know we the spirit of truth, and the spirit of error.
(3:24) And he that keepeth his commandments dwelleth in him, and he in him. And hereby we know that he abideth in us, by the Spirit which he hath given us.
(4:1) Beloved, believe not every spirit, but try the spirits whether they are of God: because many false prophets are gone out into the world.
(4:2) Hereby know ye the Spirit of God: Every spirit that confesseth that Jesus Christ is come in the flesh is of God:
(4:3) And every spirit that confesseth not that Jesus Christ is come in the flesh is not of God: and this is that spirit of antichrist, whereof ye have heard that it should come; and even now already is it in the world.
(4:4) Ye are of God, little children, and have overcome them: because greater is he that is in you, than he that is in the world.
(4:5) They are of the world: therefore speak they of the world, and the world heareth them.
(4:6) We are of God: he that knoweth God heareth us; he that is not of God heareth not us. Hereby know we the spirit of truth, and the spirit of error.