But you will receive power and ability when the Holy Spirit comes upon you; and you will be My witnesses [to tell people about Me] both in Jerusalem and in all Judea, and Samaria, and even to the ends of the earth.”

God raised this Jesus [bodily from the dead], and of that [fact] we are all witnesses.

We are [personally] eyewitnesses of everything that He did both in the land of the Jews and in Jerusalem [in particular]. They also put Him to death by hanging Him on a cross;

and for many days (forty) He appeared to those who came up with Him from Galilee to Jerusalem, the very ones who are now His witnesses to the people.

and that repentance [necessary] for forgiveness of sins would be preached in His name to all the nations, beginning from Jerusalem.

But you will testify also and be My witnesses, because you have been with Me from the beginning.

This is the third time that I am visiting you. Every fact shall be sustained and confirmed by the testimony of two or three witnesses.

how will we escape [the penalty] if we ignore such a great salvation [the gospel, the new covenant]? For it was spoken at first by the Lord, and it was confirmed to us and proved authentic by those who personally heard [Him speak],

And so

“But when the Helper (Comforter, Advocate, Intercessor—Counselor, Strengthener, Standby) comes, whom I will send to you from the Father, that is the Spirit of Truth who comes from the Father, He will testify and bear witness about Me.

But I tell you the truth, it is to your advantage that I go away; for if I do not go away, the Helper (Comforter, Advocate, Intercessor—Counselor, Strengthener, Standby) will not come to you; but if I go, I will send Him (the Holy Spirit) to you [to be in close fellowship with you].

[and besides this evidence] God also testifying with them [confirming the message of salvation], both by signs and wonders and by various miracles [carried out by Jesus and the apostles] and by [granting to believers the] gifts of the Holy Spirit according to His own will.

It was revealed to them that their services [their prophecies regarding grace] were not [meant] for themselves and their time, but for you, in these things [the death, resurrection, and glorification of Jesus Christ] which have now been told to you by those who preached the gospel to you by the [power of the] Holy Spirit [who was] sent from heaven. Into these things even the angels long to look.

Whom

And they were all filled [that is, diffused throughout their being] with the Holy Spirit and began to speak in other tongues (different languages), as the Spirit was giving them the ability to speak out [clearly and appropriately].

While Peter was still speaking these words, the Holy Spirit fell on all those who were listening to the message [confirming God’s acceptance of Gentiles].

But He was speaking of the [Holy] Spirit, whom those who believed in Him [as Savior] were to receive afterward. The Spirit had not yet been given, because Jesus was not yet glorified (raised to honor).

General references

When they bring you before the synagogues and the magistrates and the authorities, do not be worried about how you are to defend yourselves or what you are to say;

You are witnesses of these things.