John 16:12-15 (ESV Strong’s Bible)
12 “I still have many things to say to you, but you cannot bear them now.
Jesus after telling his disciples about the Holy Spirit who is the helper and what the helper will come and do, He then tells them that there are so many things that he wanted to tell them but they could not bear or handle the information at that point.
13 When the Spirit of truth comes, he will guide you into all the truth, for he will not speak on his own authority, but whatever he hears he will speak, and he will declare to you the things that are to come.
The Spirit of truth, still reffering to the Holy Spirit, Jesus told his disciples that the Holy Spirit will guide them or lead them into all truth. All truth will be revealed to them through the Holy Spirit. The Holy Spirit will not speak on his own authority but, he will speak whatever he hears. What will he hear and from who? Jesus said to his disciples in John 15:15 that all that He had heard from God, He has made known to them and Psa 25:5 tells us that it is God who leads us into his truth. This means therefore that the Holy Spirit will lead the disciples into the truth of God. God will use the Holy Spirit to lead us into His truth. So the Holy Spirit will speak what he hears from God.
Not only will He guide the disciples through all truth but He will also declare or show or make known things that are still to take place.
14 He will glorify me, for he will take what is mine and declare it to you. 15 All that the Father has is mine; therefore I said that he will take what is mine and declare it to you.
The Holy Spirit will glorify Jesus by taking what belongs to Him and making it known to his disciples. Jesus told them that all that belongs to God, belongs to Him and hence he said, the Holy Spirit will take what is His and make it known to them. This means that the Holy Spirit will make it known to them things of God.
So, therefore the work of the Holy Spirit in summary is to show the world that they are wrong in their understanding of sin, righteousness and judgement and will put the world to shame. The Holy Spirit will guide us through all truth and make known to us things that are to come. The Holy Spirit will glorify Jesus by taking what belongs to Jesus and making it known to us.