Why does Peter leave vv.19-20 of Acts 2 in his quotation of Joel 2 if those things were to happen off in the future? It’s to demonstrate that this outpouring of the Spirit points to the coming of the great and terrible Day of the Lord in which God will judge the world with comic wonders and upheavals. In other words, the purpose of this outpouring of the Spirit is to compel sinners to remember what is coming one day and to seek to be saved from it. In fact, there was an immediate judgment of God impending on these people in Jerusalem and that was coming in 70AD as prophesied by Jesus himself. This brings us to v.21, which is about salvation. You may be wondering why this appears last in the quotation, but salvation in the OT is oftentimes linked to being delivered from the judgment of the Day of the Lord. So there is a present salvation for those who call on the name of the Lord, but the ultimate salvation experience is coming since there is a future salvation yet to be realized by all believers, when they are delivered from the eternal judgment of God. And notice the promise is offered to everyone, not just devout Jews. Thus a key role of the Spirit is to highlight the salvation of Christ from judgment.
The Spirit Points to Deliverance from Judgment
