Salvation is the Divine result of believing on him, and salvation lifts the saved man from the necessity of the judgment, of the moral discrimination which awaits every man, and is passed upon every man by his own conscience and by the providence of God.
The word κρίνω does not necessarily mean "to condemn" (see John 3:17), and whensoever the unfavourable issue of judgment is emphatically referred to, then κατακρίνω is used (Romans 2:1; Romans 8:3; 1 Corinthians 11:32; Matthew 27:3).
Still, this first clause shows that the predominant sense in which it is used throughout the passage is condemnatory. He that believeth on him—i.e. whoso submits and yields to the truth confessed and conspicuous in the Christ—he who accepts the mission of the Logos, both before and after the Incarnation (see notes on John 1:12-14)—is not judged.
If there be a judgment, it is one of acquittal. In his case judgment is salvation, salvation is the judgment. Faith, affectionate confidence in the supreme Judge, transforms the judgment into mercy, anticipates the Divine and gracious result.
But he that believeth not (subjective negative) has been already judged, and is now so adjudged (here the word seems necessarily to assume a condemnatory character) that he hath not believed on the Name of the only begotten Son of God.
Such non-belief reveals insensibility to truth, indifference to the reality of things, unsusceptibility to the light, and a moral perversity which has been persisted in. The approach to such a one of the Eternal Logos did not move him, the unveiling of the Divine face did not awe him into reverence.
The sin of his life had blinded his eyes, closed his ears, hardened his heart, and the consequence was that when the Name of the only begotten Son was made known to him, like all previous Divine self-revelations, it exercised no commanding influence upon him, no convincing power, no saving grace.
To refuse Christ, to manifest unbelief under such circumstances, proves that the laws of Divine judgment which are always going on have already enacted themselves. He has been (and is) condemned. He is "judged already," and the unbelief is the judgment which the self-acting moral laws, or rather which the Logos actively at work in every human being, pronounces upon him.
The manner in which any man receives Divine revelation is the judgment passed upon his entire life up to that moment by the unerring and infallible wisdom of the supreme Judge. The final judgment is thus anticipated, but it is not irreversible, and, should repentance and faith supervene by Divine grace on this stolid indifference and damnable unbelief, the once unbeliever will become the believer, the judgment upon whom is no more a judgment of condemnation, but one of life and peace.
Nothing can indicate a more untractable, unspiritual, and carnal state than a refusal to admit so great and imposing a manifestation of the Divine nature as the Name of the only begotten Son of God.