Jesus Christ, on the night He was betrayed, told His disciples that when He would go back to the Father He would send to them the Holy Spirit, and He told them also what the Holy Spirit would do. Here are the words of Jesus: “And I will pray the Father, and he shall give you another Comforter, that he may abide with you for ever; Even the Spirit of truth; whom the world cannot receive, because it seeth him not, neither knoweth him: but ye know him; for he dwelleth with you, and shall be in you …. But the Comforter, which is the Holy Ghost, whom the Father will send in my name, he shall teach you all things, and bring all things to your remembrance, whatsoever I have said unto you ….But when the Comforter is come, whom I will send unto you from the Father, even the Spirit of truth, which proceedeth from the Father, he shall testify of me …. I tell you the truth; It is expedient for you that I go away: for if I go not away, the Comforter will not come unto you; but if I depart, I will send him unto you. And when he is come, he will reprove the world of sin, and of righteousness, and of judgment: Of sin, because they believe not on me; Of righteousness, because I go to my Father, and ye see me no more; Of judgment, because the prince of this world is judged. I have yet many things to say unto you, but ye cannot bear them now. 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” (John 14:16-17, 26; 15:26; 16:7-15). Therefore – according to the words of Jesus - the Holy Spirit would be always with His disciples, He would guide them into all truth, He would teach them all things, He would bring His words to their remembrance, He would testify about Him, He would glorify Him and tell them things to come, and would convict the world of sin, and of righteousness, and of judgment.

After Jesus was taken up into heaven and sat at the right hand of the Father, He received from the Father the promised Holy Spirit and poured out Him upon His Church. Here is what happened on the day of Pentecost, that is, a few days after His ascension to heaven: “And when the day of Pentecost was fully come, they were all with one accord in one place. And suddenly there came a sound from heaven as of a rushing mighty wind, and it filled all the house where they were sitting. And there appeared unto them cloven tongues like as of fire, and it sat upon each of them. And they were all filled with the Holy Ghost, and began to speak with other tongues, as the Spirit gave them utterance. And there were dwelling at Jerusalem Jews, devout men, out of every nation under heaven. Now when this was noised abroad, the multitude came together, and were confounded, because that every man heard them speak in his own language. And they were all amazed and marvelled, saying one to another, Behold, are not all these which speak Galilaeans? And how hear we every man in our own tongue, wherein we were born? Parthians, and Medes, and Elamites, and the dwellers in Mesopotamia, and in Judea, and Cappadocia, in Pontus, and Asia, Phrygia, and Pamphylia, in Egypt, and in the parts of Libya about Cyrene, and strangers of Rome, Jews and proselytes, Cretes and Arabians, we do hear them speak in our tongues the wonderful works of God. And they were all amazed, and were in doubt, saying one to another, What meaneth this? Others mocking said, These men are full of new wine.” (Acts 2:1-13). Peter, with regard to the above mentioned event, said these words to those Jews who came together and were all amazed and confounded: “This is that which was spoken by the prophet Joel; 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: And I will shew wonders in heaven above, and signs in the earth beneath; blood, and fire, and vapour of smoke: The sun shall be turned into darkness, and the moon into blood, before that great and notable day of the Lord come: And it shall come to pass, that whosoever shall call on the name of the Lord shall be saved” (Acts 2:16-21). Therefore, what happened on that day was nothing but the fulfilment of the promise which God had made under the Old Testament through the prophet Joel and which was confirmed by Jesus Christ in the days of His flesh.

Of course - and I have already demonstrated it - the Holy Spirit was present and worked also before the day of Pentecost, for prior to that day there were people who were filled with the Holy Spirit, who prophesied by the Holy Spirit, who predicted future events by the Holy Spirit, who wrought signs and wonders by the power of the Holy Spirit, who wrote holy books because they were moved by the Holy Spirit; but it must be pointed out that at that time the Holy Spirit had not yet been poured out upon all flesh, and also that the sign of speaking with other tongues was missing in all those who were filled with the Holy Spirit. Even Jesus Christ, when He was filled with the Holy Spirit, did not speak with other tongues, for the sign of speaking with other tongues has been marking the infilling of the Holy Spirit from the day of Pentecost on. Therefore – as far as the Holy Spirit is concerned - the day of Pentecost was the beginning of a new dispensation.