Jesus gives us His Spirit, the Holy Ghost, so that we can be witnesses.

"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 1:8

When we have repented of our sins, have been baptized in Jesus name for the remission of our sins, and are full of God’s Holy Spirit, we are to be holy.

"As obedient children, not fashioning yourselves according to the former lusts in your ignorance: but as he which hath called you is holy, so be ye holy in all manner of conversation; because it is written, Be ye holy; for I am holy." - 1 Peter 1:14-16 KJV (“So you must live as God’s obedient children. Don’t slip back into your old ways of living to satisfy your own desires. You didn’t know any better then.” 1 Peter 1:14 NLT)

According to Thayer’s Greek Lexicon, “manner of conversation” in this verse means our “'walk,' i. e. manner of life, behavior, conduct.” “Holy” in this verse means “pure, sinless, upright, holy.”

We are witnesses to the world of the Holy Ghost in us by being holy in our walk. We walk in the Spirit.

"This I say then, Walk in the Spirit, and ye shall not fulfil the lust of the flesh." - Galatians 5:16 KJV

"There is therefore now no condemnation to them which are in Christ Jesus, who walk not after the flesh, but after the Spirit." - Romans 8:1 KJV

"For they that are after the flesh do mind the things of the flesh; but they that are after the Spirit the things of the Spirit." - Romans 8:5 KJV

When Jesus gives us His Spirit, the Holy Ghost, He gives us the power we need to overcome sin in our life so we can be holy.

"But ye shall receive power, after that the Holy Ghost is come upon you: and ye shall be witnesses unto me …”

Peter preached how to receive the Holy Ghost.

"Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost.” Acts 2:38

“For the promise is unto you, and to your children, and to all that are afar off, even as many as the Lord our God shall call." - Acts 2:39