Being brought up in the AoG in the 50s and 60s we knew Acts 2.1-4 off by heart because we heard and we sang it often. In the church I was in, the choir used to sing a rendition of this passage and I can hear that choir's recital coursing through my heart's memory as I write this.
This filling with the Holy Spirit equipped the Church for service and the service was for the salvation of those around. It was not just for the edification of the apostles and disciples but for the salvation of others. That's the whole business of the gospel which is 'the power of God for salvation to everyone who believes' (Rom 1.16).
But Pentecost had been celebrated and still is within the Jewish community. Pentecost (denoting 50th day) was the 50th day after the Exodus reaching to the giving of the Law at Sinai. The day was associated with the harvest of first-fruits so one could understand the respondents to Peter's message to be an in-gathering of the First Fruits.
Interestingly this Feast is regarded as second only after Easter. Hence, although much is made of the Incarnation, Pentecost is considered more important by the Church.
Prayer
We also have today a number of strange practices abroad in the Church including praying directly to the Holy Spirit for which no biblical warrant exists. (In fact, it's hard to find any prayers in the New Testament addressed directly to the ascended Son either.) We should always pray to the Father through the Son and in the power of the Holy Spirit. All Paul's prayers follow this model.
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