During His earthly sojourn, Jesus referred to the promised Holy Spirit as the “Comforter” (John 16:7-11). The Greek word for “Comforter” means “Counselor.” In Jesus’ day, this word was used to refer to legal assistants who presented, pleaded and proved cases in court.
According to Jesus, the coming of the Holy Spirit would put the whole world on trial. The defendants in the case would be the earth’s inhabitants. The witnesses in the case would be Christians. Remember, Jesus promised that we would be His witnesses once the Holy Spirit came, not before (Acts 1:8). The Judge would be Christ Himself, to whom the Father has committed all judgment (John 5:22). And the prosecuting attorney or “Counselor” would be the Holy Spirit. The Holy Spirit would come into the world to convict the world of sin and to convince it of its need of the Savior.
Although you and I can witness for Christ, only the Holy Spirit can prove to man God’s case against him. This explains why Jesus told His disciples that “it [was] expedient for [them] that [He] go away: for if [He didn’t] go away, the Counselor [would] not come unto [them].” Without the Counselor, God’s case against sinners cannot be proven to them, no matter how good the witnesses are. It takes the closing argument of the Holy Spirit to persuade sinners to confess their sins to God and to throw themselves on the mercy of the heavenly court.
During His earthly ministry, Jesus knew that it would do no good for His disciples to tell others who He was; after all, without the Holy Spirit to confirm the disciples’ confession of Christ others would be unconvinced by their witness. Thus, He often instructed His disciples and others not to tell (Matthew 8:4; 9:30; 12:16; 16:20; Mark 5:43; 7:36; 8:30). Even after His resurrection and just prior to His ascension Jesus instructed His disciples to go to Jerusalem and wait for the coming of the Holy Spirit (Acts 1:4). It was not until the Holy Spirit came that they were empowered to be His witnesses and enabled to fulfill the Great Commission by going into all of the world with the Gospel.