Let's begin with the prophecies of Joel:
And it shall come to pass afterward, that I will pour out my spirit upon all flesh; and your sons and your daughters shall prophesy, your old men shall dream dreams, your young men shall see visions: And also upon the servants and upon the handmaids in those days will I pour out my spirit. And I will shew wonders in the heavens and in the earth, blood, and fire, and pillars of smoke. The sun shall be turned into darkness, and the moon into blood, before the great and the terrible day of the LORD come. And it shall come to pass, that whosoever shall call on the name of the LORD shall be delivered: for in mount Zion and in Jerusalem shall be deliverance, as the LORD hath said, and in the remnant whom the LORD shall call.
(
Joel 2:28-32 KJV)
As quoted from the Greek LXX used by Peter:
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 2:17-21 KJV)
What was going to happen? The key part is "
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."
There are 7 categories of recipients of the Spirit that are mentioned: all flesh, your sons, your daughters, your old men, your young men, the (my) servants, and the (my) handmaids. The Spirit would be poured out upon 'all flesh', meaning 'everyone'. The following six categories are subdvisions of the 'all flesh'. That means sons, daughters, old men, young men, servants, and handmaidens. Now, all the 'sons' would be all the males, of any age. And all the 'daughters' would be all the females, of any age. Old men and young men are two particular categories of the males, but pretty much covers all the males. Servants are all the males who serve God, and handmaidens are all the females who serve God. Notice, the "young me"n and the "old men" are included in the categories of "sons" and "servants". The "sons" comprise all the males, as does the "servants". They are both the same group - the males. The "daughters" and the "handmaids" likewise are the same group, since both groups are synomyous with 'all the females'.
Each of these categories were to experience something as a result of receiving the Spirit: the sons and daughters were to 'prophesy', the young men were to 'see visions', the old men were to 'dream dreams', and the servants and the handmaids were to 'prophesy'. So we see that all the males ("sons" and "servants") were to "prophesy", and all the females ("daughters" and "handmaids") likewise were to "prophesy". (The old men and the young men are included in the groups of servants and sons.) So there was to be a universal outpouring of the Spirit, and every possible category of person who would receive the Spirit would experience the same thing: they would 'prophesy'.
Thus, according to Joel, there was to be a universal 'evidence' or 'sign' of the Spirit being received: each person who received the Spirit was to 'prophesy'.
What does 'prophesy' mean? Why, it means to 'speak the words that God gives you to speak.' It generally means 'ecstatic utterance', it most definitely means speaking forth whatever the Spirit of God leads you to speak. So, the initial evidence, if you will, according to Joel was that people - ALL people - who receive the Spirit would 'prophesy', or speak whatever God gave them to speak.
Now, what actually happened when this came to pass?
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.
(Acts 2:1-4 KJV)
There was a sound like a strong wind, and there were visions of cloven tongues of fire coming down and sitting upon the disciples, but these things happened BEFORE anyone received the Spirit. When they were 'all filled with the Holy Ghost', they 'began to speak with other tongues as the Spirit gave them utterance'.
Each person received the Spirit, and each person began to speak in tongues.
But wait. Joel said they would 'prophesy', yet we see them 'speaking with tongues'. How do we resolve this dilemma, this discrepancy? Notice what Peter said: 'This is that which was spoken by the prophet Joel.'
This is
that.
What is what?
This means the disciples being filled with the Holy Ghost and speaking in tongues.
That means the outpouring of God's Spirit upon all his male and female servants and them prophesying. The outpouring of the Spirit is fulfilled in the disciples being filled with the Holy Ghost. And the 'prophesying' is fulfilled in the 'speaking with other tongues as the Spirit gave them utterance'.
This means that the universal sign clearly stated by Joel is fulfilled by 'speaking with other tongues as the Spirit gives the utterance'.
This means that there is a prophesied, old testament expectation of a universal sign or evidence of receiving the Spirit, and the new testament clearly and unambiguously identifies that evidence as 'speaking with tongues.' In other words, the 'initial evidence doctrine' is found in both the old testament and the new testament.
Now, what exactly was going on in that upper room?
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.
(
Acts 2:5-6 KJV)
The multitude that gathered showed up
after the tongue speaking had commenced. So we can rule out that specious and silly notion that the disciples were speaking in tongues in order to preach to foreignors. But notice carefully what is said: "...because that every man heard them speak in his own language."
Read that again: EVERY man heard THEM speak in HIS OWN language. I'll repeat that for emphasis:
EVERY man heard THEM speak in HIS OWN language
The common idea is that some disciples were speaking one language, some another, and so forth. But that is not what the text says. It says that each person in the crowd who gathered to see what was going on, heard EVERY DISCIPLE speaking in HIS OWN NATIVE LANGUAGE. Let me repeat that for emphasis:
EACH PERSON in the crowd who gathered to see what was going on, heard EVERY DISCIPLE speaking in HIS OWN NATIVE LANGUAGE.
So the guy from Libya heard EVERY DISCIPLE speaking in Libyan. But the guy from Rome heard EVERY DISCIPLE speaking Latin. And the guy from Greece heard EVERY DISCIPLE speaking Greek. And so forth.
Think on that for a moment. Picture it in your mind. Try to imagine Peter speaking Latin, Greek, Libyan, Phrygian, and however many other languages were represented there - ALL AT THE SAME TIME. And imagine each of the other disciples there doing the exact same thing.
IMPOSSIBLE you say? Yes, it is biologically impossible for a person to simultaneously speak multiple languages AT THE SAME TIME. When a word comes out of your mouth, it will be in one or another language, but not both, or three, or ten.
The disciples were speaking in tongues before anyone showed up to ooh and ahh. So there they are, speaking in tongues. The whole lot of them, all at the same time. A crowd showed up to see what was going on, and lo and behold EACH PERSON in the crowd hears ALL THE DISCIPLES speaking in his own native language. And the crowd is 'confounded'. Indeed, so would you be 'confounded' in such a situation.
IF one disciple was speaking one language, and another disciple speaking another language, and so forth, would you be confounded? No, you might be amused but not confounded. Confounded means 'utterly clueless as to how something can be happening'. Stunned. Blown away. Astonished. Astonied (as the KJV puts it).
BUT WAIT, there's more. Some folks showed up and were NOT confounded at all. They knew exactly what was going on. 'These guys are DRUNK.' They are mad, they are on crack.
And isn't that what Paul said would happen if the UNBELIEVING came in to the midst of a meeting where everyone is 'speaking with tongues'?
If therefore the whole church be come together into one place, and all speak with tongues, and there come in those that are unlearned, or unbelievers, will they not say that ye are mad?
(
1 Corinthians 14:23 KJV)
So how did all those 'devout men' hear every single disciple speaking HIS OWN language, when these disciples were simply 'speaking in tongues'? Apparently God caused them to hear in their own language. Is this too much? Well, was it too much for a sound like a rushing mighty wind, or cloven tongues of fire? Was it too much for the three lepers whose footsteps God amplified into the sound of an approaching army that none but the Syrians could hear in 2 Kings chapter 7?
So then, not only is speaking with tongues the Biblically documented universal, initial evidence of receiving the Holy Ghost, it is also not about speaking in languages known to the hearers.
For he that speaketh in an unknown tongue speaketh not unto men, but unto God: for no man understandeth him; howbeit in the spirit he speaketh mysteries.
(
1 Corinthians 14:2 KJV)
No man understandeth him... unless God gives a supernatural understanding of what is being said... unless God causes you to hear it in a way that makes sense to you...