Jn 14:26, Jn 15:26, Jn 16:13, Acts 1:8
The main work of the Holy Spirit is to testify that Jesus is the Christ. The Holy Spirit works on the saints so that they can testify that Jesus is the Christ. (Mk 13:10-11)
Mk 13:10 And the gospel must first be published among all nations. 11 But when they shall lead you, and deliver you up, take no thought beforehand what ye shall speak, neither do ye premeditate: but whatsoever shall be given you in that hour, that speak ye: for it is not ye that speak, but the Holy Ghost.
The Holy Spirit reminds us of what Jesus said during his public life so that we can realize that Jesus is the Christ. (Jn 14:26, Jn 15:26, Jn 16:13)
Jn 14:26 But the Comforter, which is the Holy Ghost, whom the Father will send in my name, he shall teach you all things, and bring all things to your remembrance, whatsoever I have said unto you.
Jn 15:26 But when the Comforter is come, whom I will send unto you from the Father, even the Spirit of truth, which proceedeth from the Father, he shall testify of me:
Jn 16:13 Howbeit when he, the Spirit of truth, is come, he will guide you into all truth: for he shall not speak of himself; but whatsoever he shall hear, that shall he speak: and he will shew you things to come.
When the Holy Spirit comes upon us, we will spread the gospel that Jesus is the Christ all over the world. (Acts 1:8)
Acts 1:8 But ye shall receive power, after that the Holy Ghost is come upon you: and ye shall be witnesses unto me both in Jerusalem, and in all Judaea, and in Samaria, and unto the uttermost part of the earth.