John Calvin on John 3:18

18. He who believeth in him is not condemned. When he so frequently and so earnestly repeats, that all believers are beyond danger of death, we may infer from it the great necessity of firm and assured confidence, that the conscience may not be kept perpetually in a state of trembling and alarm. He again declares that, when we have believed, there is no remaining condemnation, which he will afterwards explain more fully in the Fifth Chapter. The present tense — is not condemned — is here used instead of the future tense — shall not be condemned — according to the custom of the Hebrew language; for he means that believers are safe from the fear of condemnation.

But he who believeth not is condemned already This means that there is no other remedy by which any human being can escape death; or, in other words, that for all who reject the life given to them in Christ, there remains nothing but death, since life consists in nothing else than in faith. The past tense of the verb, is condemned already, (ἤδη κέκριται,) was used by him emphatically, (ἐμφατικῶς,) to express more strongly that all unbelievers are utterly ruined. But it ought to be observed that Christ speaks especially of those whose wickedness shall be displayed in open contempt of the Gospel. For though it is true that there never was any other remedy for escaping death than that men should betake themselves to Christ, yet as Christ here speaks of the preaching of the Gospel, which was to be spread throughout the whole world, he directs his discourse against those who deliberately and maliciously extinguish the light which God had kindled.

John 3:19-21

19. And this is the condemnation, that light is come into the world; and men loved darkness rather than light; for their works were evil. 20. For whosoever doeth what is evil hateth the light, and cometh not to the light, that his works may not be discovered. 21. But he who doeth truth cometh to the light, that his works may be made manifest, that they are done in God. “Faites selon Dieu;” — “done according to God.”