Jesus told the disciples that He was going to leave to return to the Father, the One who sent Him. But, when He goes He will send the Advocate from the Father to be with the believers. The disciples were not to leave Jerusalem until they received the promised gift from the Father a few days after He was taken up into heaven in a cloud.
When they received the gift of baptism in the Holy Spirit they will receive power and be able to tell others about Jesus Christ. To be His witnesses and share Jesus Christ with all people everywhere, to the ends of the earth. The Spirit of Truth will convict the world, the unbelievers of their sin so that they will repent and be saved into the righteousness through Jesus Christ for the coming Judgement.
Believers have a glimpse of the future glory of His Kingdom by the Spirit, as they long patiently and confidently for the day when God will give His adopted children full rights united into His Kingdom. Until Jesus returns, the Advocate, Holy Spirit of truth will reveal the truth to us as He heard from the Father and received from Jesus Christ. The Holy Spirit of the believers Helper, Comforter and Guide.
When we do not know what God wants us to pray, the Holy Spirit prays for us, pleads for us before God with groans that the Father understands as He knows all hearts, in harmony with His will for us. Today, we as believers are equipped with the gifts of the Holy Spirit to do the work God willed for us as part of His Body. He teaches us, helps us resist temptation and sin and helps us produce fruit of the Spirit in our lives.
Lots of Blessings.