7 Nevertheless I tell you the truth. It is to your advantage that I go away; for if I do not go away, the Helper will not come to you; but if I depart, I will send Him to you. 8 And when He has come, He will convict the world of sin, and of righteousness, and of judgment: 9 of sin, because they do not believe in Me; 10 of righteousness, because I go to My Father and you see Me no more; 11 of judgment, because the ruler of this world is judged. (John 16:7–11, NKJV)
The Holy Spirit is “the Helper” Jesus promised to send to His apostles, who would “guide them into all truth” (Jno. 16:13). Jesus kept His promise on the Day of Pentecost (Acts 1:4-5, 8; 2:1-4). By the preaching of the apostles, the Holy Spirit began convicting the world of sin, of righteousness and of judgment. By their word, the Spirit of God convicted the audience of their sin (“Now when they heard this, they were cut to the heart,” Acts 2:37). He convinced them how to become servants of righteousness (“repent,…and be baptized,” Acts 2:38). And, he convinced them of judgment (“save yourselves,” Acts 2:40, ESV). The Holy Spirit continues to convict the world by the inspired message of the apostles, and by it, to save those who believe (1 Cor. 1:21).