Instead of the bogus glossolalia and "slain in the spirit" aberrations, the Holy Spirit empowers us to keep God's law in spirit as well as in the letter. Ancient Israel was unable to keep the terms of the Old Covenant because their hearts were not right. On Pentecost, God gave His Spirit to a remnant of Israel, providing them with a heart to keep His Law, enabling them to become sanctified and separated from the world, and providing a witness to the rest of the world.