A Witness must:-

a] Have seen the things for themselves
Act 1:3 "To whom also he shewed himself alive after his passion" That is, after his sufferings and death; for that he suffered many things, and at last death itself, is certain from the acknowledgment of the Jews themselves, who own, that they put him to death on the Passover eve "by many infallible proofs, being seen of them forty days, and speaking of the things pertaining to the kingdom of God:" "And when he had spoken these things, while they beheld, he was taken up; and a cloud received him out of their sight." Acts 1:9

b] Appear in public
Act 2:14 "...Peter, standing up with the eleven, lifted up his voice, and said unto them, Ye men of Judaea, and all ye that dwell at Jerusalem, be this known unto you, and hearken to my words" Peter, as their mouth, stood "in the midst" of them, with great courage, boldness, and intrepidity of mind: and "lift up his voice"; that he might be heard by the whole multitude, that was gathered together, as well as to show his zeal and fervour of spirit, and fortitude of mind; for being endued with the Spirit from on high, he was fearless of men, who but a little while ago was frightened by a servant maid,

c] Faithfully report the facts.
The people knew the facts
Acts 2:22 - 24 "....hear these words; Jesus of Nazareth, a man approved of God among you by miracles and wonders and signs, which God did by him in the midst of you, as ye yourselves also know: Him, being delivered by the determinate counsel and foreknowledge of God, ye have taken, and by wicked hands have crucified and slain: Whom God hath raised up, having loosed the pains of death: because it was not possible that he should be holden of it".

So in Acts 1-8 our witness has
A] A central Theme ME
B] An expanding Sphere JERUSALEM ------Home [acts chs 1-7]
JUDEA--------------Our towns folk [8-9]
SAMARIA--Our enemies and country ''
UTTERMOST PARTS -Wide World [10-28]
C] Its only Source THE HOLY SPIRIT
D] Its Unfailing Secret THE POWER OF THE HOLY SPIRIT

1] The Duration of our Witness
From Christ's ascension till His return.
Act 1:7 "And he said unto them, It is not for you to know the times or the seasons, which the Father hath put in his own power". Act 1:9-11 "And when he had spoken these things, while they beheld, he was taken up; and a cloud received him out of their sight. And while they looked steadfastly toward heaven as he went up, behold, two men stood by them in white apparel; Which also said, Ye men of Galilee, why stand ye gazing up into heaven? this same Jesus, which is taken up from you into heaven, shall so come in like manner as ye have seen him go into heaven".

2] The Direction of our Witness
Acts 1:8b "ye shall be witnesses unto me both in Jerusalem, and in all Judea, and in Samaria, and unto the uttermost part of the earth.

3] The Dynamic of our Witness
Power after the Holy Spirit Acts 1:8a ".... ye shall receive power after that the Holy Ghost is come upon you:"