John 16:9

Of sin, because they believed (believe, Greek and Syriac version) not in Me. He will convict My enemies, both Jewish and Gentile unbelievers, both of the great sin of unbelief (S. Chrysostom and Augustine), and of every other sin (S. Cyril), for refusing to believe in Me, after the many reasons they have heard, and the miracles they have seen. For the Spirit will bring home to them the state of their soul, both outwardly, by earnest preaching, by the sanctity of the Apostles, and the miracles He will work through them; and inwardly, by enlightening their minds by His Inspiration, so that they will acknowledge, even against their will, that they are in their former infidelity and other sins, and that they cannot be liberated from them, except by faith in Me, which they refused to accept. For He will demonstrate to them that there is no other Saviour who can atone for sin, but Myself. See Acts iv. 12. And consequently, though many were moved by this preaching of the Apostles, yet others, by persisting in their unbelief, became inexcusable, and worthy of damnation and hell. See Acts ii. 37. So S. Cyril, Leontius, and others. Ver. 10. Of righteousness. The Holy Spirit will prove that the righteousness of the world is false; that of the Jews, because they sought it by the ceremonies of the Law, which could not purify the soul; and that of the Gentiles, because they sought it only in things which were naturally and morally honest, and despised Christ. But He, the Holy Ghost, will set forth Christ, who was despised and counted unrighteous, to be alone Righteous, and the source and origin of all righteousness. So S. Cyril, lib. vi.

Tropologically, S. Bernardine (Serm. xxi.) says, "The Holy Spirit reproves the world of sin, because it dissembles; of righteousness, which it does not order rightly, while it gives it to itself and not to God; of judgment, which it usurps, in rashly judging both of itself and others."

Because I go to My Father. It is an offence to the world, and worldlings, that, seeming to be a mere man, I preach new and paradoxical doctrines. But the contrary will soon be made manifest to them, viz., that I have been sent by God the Father to reconcile the world to God by My death on the Cross, and to raise them to the rights of His children. For, ascending unto heaven I shall return to Him, so that the world will see Me no more, nor be scandalised by the sight of My infirmity in the flesh. And I will from thence send the Holy Spirit to justify and sanctify those who believe in Me, and from this it will be clear to the whole world that I am not a mere man, but the God-man, the justifier and Sanctifier of the world. So Leontius, S. Chrysostom, Theophylact, and Euthymius. S. Chrysostom adds that the Holy Spirit distributed His gifts and graces to the faithful at the invocation of the Name of Jesus.

And ye will see Me no more. He speaks not of them personally, but of men in general. Ye will see Me ascending to My Father, but afterwards ye will see Me no more in this life. So Maldonatus, Ribera, and others.

Toletus adds that Christ said this, to signify that there was no need for Him to come again into the world, to suffer and to die. For by My death once for all I have fulfilled all righteousness for all men, past, present, and to come. Ye will therefore see Me no more as ye have hitherto seen Me. Having then completed all righteousness, the world must after My departure be at once convicted of righteousness, that is to say, that it has been completed and consummated by Me. S. Augustine (in loc.) adds, "The world is reproved of sin, because it believes not in Christ. It is reproved too concerning the righteousness of those who believe; for to compare the faithful with unbelievers is to blame the unbelieving. But because it is the common cry of unbelievers, 'How can we believe that which we do not?' He therefore defined the righteousness of those who believe, in these words, 'Because I go to My Father, and ye shall see Me no more. Blessed are they who do not see and yet believe.' This then will be your righteousness, of which the world is reproved, that ye believe in Me, whom ye will not see." He says also (de Verb. Dom. Serm. lxi.), "They believed not, but He goes to the Father. It was their sin, but His righteousness. For His coming to us was an act of mercy, His going to the Father was His righteousness," as the apostle said, "Wherefore God hath also highly exalted Him." And also (Quæs. N. et V. Test. xxxix.), "By His returning He proved that He had come from thence." And S. Chrysostom, "His going to the Father was a proof that He had lived a blameless life, so that they could not say, He is a sinner, and is not from God."