The main purpose of the Holy Ghost is to give you power to be a witness to others for Jesus. This is why we need the Holy Spirit. The more you follow Jesus, the more anointing of the Holy Ghost you will receive.
John 1:12 -But as many as received him, to them gave he power to become the sons of God, even to them that believe on his name.
John 7:38-39 - He that believeth on me, as the scripture hath said, out of his belly shall flow rivers of living water. (But this spake he of the Spirit, which they that believe on him should receive: for the Holy Ghost was not yet given; because that Jesus was not yet glorified.)
John 16:13-16 - Howbeit when he, the Spirit of truth, is come, he will guide you into all truth: for he shall not speak of himself; but whatsoever he shall hear, that shall he speak: and he will shew you things to come. He shall glorify me: for he shall receive of mine, and shall shew it unto you. All things that the Father hath are mine: therefore said I, that he shall take of mine, and shall shew it unto you. A little while, and ye shall not see me: and again, a little while, and ye shall see me, because I go to the Father.
Luke 11:10-13 For every one that asketh receiveth; and he that seeketh findeth; and to him that knocketh it shall be opened. If a son shall ask bread of any of you that is a father, will he give him a stone? or if he ask a fish, will he for a fish give him a serpent?Or if he shall ask an egg, will he offer him a scorpion? If ye then, being evil, know how to give good gifts unto your children: how much more shall your heavenly Father give the Holy Spirit to them that ask him?
Acts 1:8 - But ye shall receive power, after that the Holy Ghost is come upon you: and ye shall be witnesses unto me both in Jerusalem, and in all Judaea, and in Samaria, and unto the uttermost part of the earth.
Acts 2:17-18 - And it shall come to pass in the last days, saith God, I will pour out of my Spirit upon all flesh: and your sons and your daughters shall prophesy, and your young men shall see visions, and your old men shall dream dreams: And on my servants and on my handmaidens I will pour out in those days of my Spirit; and they shall prophesy:
Acts 4:31 - And when they had prayed, the place was shaken where they were assembled together; and they were all filled with the Holy Ghost, and they spake the word of God with boldness.
Acts 5:32 - And we are his witnesses of these things; and so is also the Holy Ghost, whom God hath given to them that obey him.