"The Holy Spirit's work is to complete and sustain what God the Father has planned and what God the Son has begun."- Wayne Grudem, Systematic Theology, page 635
Part of what the Holy Spirit does is to empower, teach, and illuminate.
Illuminate means that it is through the Holy Spirit that we understand the scripture. "The man without the Spirit does not accept the things that come from the Spirit of God, for they are foolishness to him, and he cannot understand them, because they are spiritually discerned." 1 Corinthians 2:14 (NIV)
Teaching means that the Holy Spirit will guide us to truth (although this does not mean we bypass hardship, pain or suffering). "I have much more to say to you, more than you now can hear. But when he, the Spirit of Truth, comes, he will guide you into all truth." John 16:12-13 (NIV)
Empowers us means the Holy Spirit gives us the gifts we need to do God's will. "We have different gifts, according to the grace given us. If a man's gift is prophesying, let him use it in proportion to his faith. If it is serving, let him serve; it it is teaching, let him teach; if it is encouraging, let him encourage; if it is contributing to the needs of others, let him give generously; if it is leadership, let him govern generously; if it is showing mercy, let him do so cheerfully." Romans 12:6-8 (NIV)