1 John 1:5

5This then is the message, or promise. I do not disapprove of the rendering of the old interpreter, “This is the annunciation,” or message; for though ἐπαγγελία means for the most part a promise, yet, as John speaks here generally of the testimony before mentioned, the context seems to require the other meaning, except you were to give this explanation, “The promise which we bring to you, includes this, or has this condition annexed to it.” Thus, the meaning of the Apostle would become evident to us. (60) For his object here was not to include the whole doctrine of the Gospel, but to shew that if we desire to enjoy Christ and his blessings, it is required of us to be conformed to God in righteousness and holiness. Paul says the same thing in the second chapter of the Epistle to Titus, “Appeared has the saving grace of God to all, that denying ungodliness and worldly lusts, we may live soberly and righteously and holily in this world;” except that here he says metaphorically, that we are to walk in the light, because God is light.

But he calls God light, and says that he is in the light; such expressions are not to be too strictly taken. Why Satan is called the prince of darkness is sufficiently evident. When, therefore, God on the other hand is called the Father of light, and also light, we first understand that there is nothing in him but what is bright, pure, and unalloyed; and, secondly, that he makes all things so manifest by his brightness, that he suffers nothing vicious or perverted, no spots or filth, no hypocrisy or fraud, to lie hid. Then the sum of what is said is, that since there is no union between light and darkness, there is a separation between us and God as long as we walk in darkness; and that the fellowship which he mentions, cannot exist except we also become pure and holy.

In him is no darkness at all. This mode of speaking is commonly used by John, to amplify what he has affirmed by a contrary negation. Then, the meaning is, that God is such a light, that no darkness belongs to him. It hence follows, that he hates an evil conscience, pollution, and wickedness, and everything that pertains to darkness.