About 400 years before Christ, God made a promise to all of humanity through the prophet Joel, a promise that was in response to the great longing in Moses' heart:
"If only all Yahweh's people were prophets,
and Yahweh had given them his spirit!" (Num.11:29)
This happened at a time when the multitude of Hebrews that Moses was leading through the desert to the Promised Land were complaining about everything. Moses was very tired and weighed down so he himself went and talked to the Lord, telling Him that he couldn't carry these people any more. It was so bad for him that he actually wanted God to kill him! The Lord, always gracious and kind, told him to gather 70 elders who would bear the burden of the people with him. God promised that He would pour out His spirit upon all 70 men, thus anointing them with the same wisdom, insights and knowledge that Moses had.
The day came and God took some of the spirit that was on Moses and put it on the 70 elders, so that they too began too prophesy. Sadly though, they only prophesied once! But they did receive gifts of wisdom in order to help Moses govern the people. Now, two men had stayed back in the camp but the Holy Spirit fell on them too, prompting Joshua to want these men stopped. But this is when Moses made his famous reply. Moses wasn't jealous at all; he wished that all would have the Spirit as he did!
About 850 years later, God raised up the prophet Joel, and had him declare prophetically that Moses' prayer would indeed one day come to pass:
"I shall pour out my spirit on all humanity.
Your sons and daughters shall prophesy,
your old people shall dream dreams,
and your young people see visions.
Even on the slaves, men and women,
shall I pour out my spirit in those days."
This promise was fulfilled on the day of Pentecost following the resurrection of Jesus when all those who were gathered to "wait" received the long-awaited gift: the outpouring of the Holy Spirit upon all people.
Peter's discourse in Acts 2:16-21 clearly confirms the miracle of Pentecost as the fulfillment of Joel's prophecy. Therefore, as sons and daughters of the Father and as believers in Jesus Christ, this baptism in the Spirit is our heritage; it is ours to claim without any trace of doubt and with great joy.