From this website.
Christ was sent by God to accomplish an extremely critical mission. The main purpose of that mission was to create a way through which humanity can be brought back to God and inherit eternal life. Glory to God, it was a mission that was fulfilled successfully and victoriously when He willingly gave His life and came back to life after three days.
With that being said, there’s another vital work that must be carried out in the life of those who have accepted Him as their personal Savior and Lord. And it’s an ongoing life-changing transformation that must be transpired. It’s the very transformation that will show plainly both the transformative and regenerating power of Christ’s death on people’s lives (2 Corinthians 5:17). That’s the key reason the Holy Spirit is sent by God to come and indwell those that believe in His only Son. His job is to empower us daily, so that we can live a victorious, fulfilling, and fruitful life for the glory of God.
Prior to Christ’s ascension to heaven, He had such a great conversation with His disciples concerning someone whose coming was imminent. He said to them that He will ask the Father to send them another advocate (John 14:16). The term “another” means someone who is just like Him. Someone who will be as loving, caring, protective, and supportive as He is. He did speak about various functions that person will play in their lives. So among these are leading them into all truth, reminding them of everything He said, and teaching and helping them to understand the Word of God.
The Holy Spirit is the agent who’s working through us constantly in order to transform us day by day to become the very person that God wants us to be. He’s the One who bears witness with our own human spirit that we’re children of God (Romans 8:16). It’s safe to conclude that He’s the One reminding us of whom we are in Christ. He’s the One who empowers us to resist Satan and his field of temptation. He’s the One who reveals Christ to us. Lastly, the life that we must live through Christ revolves around what He’s doing through us for the glory of God. See without faith it is impossible to please God.