Of sin, because they believe not on me;

People's New Testament

16:9 Of sin, because they believe not on me. In naming sin, the chief of all sins is singled out. All sin springs from unbelief. To destroy sin, the heart of man must be pierced with the sword of the Spirit. Hence, the aim of the Spirit on Pentecost, and always, is to destroy unbelief.

Wesley's Notes

16:9 Of sin - Particularly of unbelief, which is the confluence of all sins, and binds them all down upon us.

Jamieson-Fausset-Brown Bible Commentary

9. Of sin, because they believe not on me-As all sin has its root in unbelief, so the most aggravated form of unbelief is the rejection of Christ. The Spirit, however, in fastening this truth upon the conscience, does not extinguish, but, on the contrary, does consummate and intensify, the sense of all other sins.

Matthew Henry's Concise Commentary

16:7-15 Christ's departure was necessary to the Comforter's coming. Sending the Spirit was to be the fruit of Christ's death, which was his going away. His bodily presence could be only in one place at one time, but his Spirit is every where, in all places, at all times, wherever two or three are gathered together in his name. See here the office of the Spirit, first to reprove, or to convince. Convincing work is the Spirit's work; he can do it effectually, and none but he. It is the method the Holy Spirit takes, first to convince, and then to comfort. The Spirit shall convince the world, of sin; not merely tell them of it. The Spirit convinces of the fact of sin; of the fault of sin; of the folly of sin; of the filth of sin, that by it we are become hateful to God; of the fountain of sin, the corrupt nature; and lastly, of the fruit of sin, that the end thereof is death. The Holy Spirit proves that all the world is guilty before God. He convinces the world of righteousness; that Jesus of Nazareth was Christ the righteous. Also, of Christ's righteousness, imparted to us for justification and salvation. He will show them where it is to be had, and how they may be accepted as righteous in God's sight. Christ's ascension proves the ransom was accepted, and the righteousness finished, through which believers were to be justified. Of judgment, because the prince of this world is judged. All will be well, when his power is broken, who made all the mischief. As Satan is subdued by Christ, this gives us confidence, for no other power can stand before him. And of the day of judgment. The coming of the Spirit would be of unspeakable advantage to the disciples. The Holy Spirit is our Guide, not only to show us the way, but to go with us by continued aids and influences. To be led into a truth is more than barely to know it; it is not only to have the notion of it in our heads, but the relish, and savour, and power of it in our hearts. He shall teach all truth, and keep back nothing profitable, for he will show things to come. All the gifts and graces of the Spirit, all the preaching, and all the writing of the apostles, under the influence of the Spirit, all the tongues, and miracles, were to glorify Christ. It behoves every one to ask, whether the Holy Spirit has begun a good work in his heart? Without clear discovery of our guilt and danger, we never shall understand the value of Christ's salvation; but when brought to know ourselves aright, we begin to see the value of the Redeemer. We should have fuller views of the Redeemer, and more lively affections to him, if we more prayed for, and depended on the Holy Spirit.