Who is the Holy Spirit? The Holy Spirit is God. God is three persons in one, which is difficult for us to get our minds around. There is God the Father, God the Son, and God the Holy Spirit. The Holy Spirit is the third person of the Trinity.
When the angel Gabriel visited Mary, he told her she would have a child by the Holy Spirit. Mary would experience something no woman before or after has experienced. Matt. 1:18 This is how Jesus the Messiah was born. His mother, Mary, was engaged to be married to Joseph. But before the marriage took place, while she was still a virgin, she became pregnant through the power of the Holy Spirit. 
Part of the work of the Holy Spirit was to enable Jesus to be conceived by the third person of the Trinity. The Holy Spirit would be at work in the life of Mary throughout her life. Mary is a wonderful example of cooperating with the work of the Holy Spirit in her life even when she did not understand. As humans we may not always understand where the Lord is leading us or what He is doing. Like Mary we must simply move forward in faith, which is trust in God.
What else does the Bible tell us about the Holy Spirit?
When we believe in Jesus as our Savior, the Holy Spirt comes and lives in us. The Lord tells us He will never leave us. John 14:16 And I (Jesus) will ask the Father, and he will give you another Advocate, who will never leave you. 17 He is the Holy Spirit, who leads into all truth. The world cannot receive him, because it isn’t looking for him and doesn’t recognize him. But you know him, because he lives with you now and later will be in you.
The Holy Spirit helps to transform you. 2 Cor. 3:18 So all of us who have had that veil removed can see and reflect the glory of the Lord. And the Lord—who is the Spirit—makes us more and more like him as we are changed into his glorious image. 
As a result of the Holy Spirit working in our hearts God’s Spirit can give us insight that only comes from Him. We can supernaturally receive revelations or insights to help us fulfill the plans the Lord has for us. Others may think we are very wise, but it is God who is wise. We are just vessels of the Holy Spirit.
Respond to the Holy Spirit
Ask the Lord to help you be sensitive to the work of the Spirit in your life. Be ready for His transforming power to begin to work in your daily life. And remember that through Him, there are no limits. Who is the Holy Spirit? Find out more here: