Witnessing: Prepared by God to tell about Jesus, we see what God does and understand our purpose (Acts)

When we're prepared by God

John baptized with water, but in just a few days you will be baptized with the Holy Spirit.” Acts 1:5

...dates and times are not for you to know. But you will receive power when the Holy Spirit comes upon you. And you will be my witnesses, telling people about me everywhere Acts 1:6-8

When we tell people about Jesus:

Peter replied, "Repent and be baptized, every one of you, in the name of Jesus Christ for the forgiveness of your sins, and you will receive the gift of the Holy Spirit. Acts 2:38

We witness what God does:

“But the voice from heaven spoke again: ‘Do not call something unclean if God has made it clean.’ This happened three times before the sheet and all it contained was pulled back up to heaven.

“Just then three men who had been sent from Caesarea arrived at the house where we were staying. The Holy Spirit told me to go with them and not to worry that they were Gentiles. These six brothers here accompanied me, and we soon entered the home of the man who had sent for us. He told us how an angel had appeared to him in his home and had told him, ‘Send messengers to Joppa, and summon a man named Simon Peter. He will tell you how you and everyone in your household can be saved!’

“As I began to speak,” Peter continued, “the Holy Spirit fell on them, just as he fell on us at the beginning. Then I thought of the Lord’s words when he said, ‘John baptized with water, but you will be baptized with the Holy Spirit.’ And since God gave these Gentiles the same gift he gave us when we believed in the Lord Jesus Christ, who was I to stand in God’s way?”

When the others heard this, they stopped objecting and began praising God. They said, “We can see that God has also given the Gentiles the privilege of repenting of their sins and receiving eternal life.” Acts 11:9-18

Then we realize Witnessing is about understanding why God placed us here. 

I did not shrink back from declaring anything that was helpful to you... one message... the necessity of repenting from sin and turning to God, and of having faith in our Lord Jesus. 

“And now I am bound by the Spirit to go... I don’t know what awaits me, except that the Holy Spirit tells me... my life is worth nothing to me unless I use it for finishing the work assigned me by the Lord Jesus—the work of telling others the Good News about the wonderful grace of God. (Eph 2:10)

... I didn’t shrink from declaring all that God wants you to know.

“So guard yourselves and God’s people. Feed and shepherd God’s flock—his church, purchased with his own blood—over which the Holy Spirit has appointed you as leaders. I know that false teachers, like vicious wolves (Matthew 7:15), will come in among you after I leave, not sparing the flock. Even some men from your own group will rise up and distort the truth in order to draw a following. Watch out! Remember the three years I was with you—my constant watch and care over you night and day, and my many tears for you.

•  - Marks of the false teacher: cause dissensions and hindrances, slaves to own appetites, smooth and flattering speech they deceive the hearts of the unsuspecting (Romans 16:17–18).  “deceitful spirits” who advocate “doctrines of demons” (1 Timothy 4:1) and as those “who will secretly introduce destructive heresies, even denying the Master who bought them” (2 Peter 2:1). false brothers (2 Corinthians 11:26); false apostles (2 Corinthians 11:13); false teachers (2 Peter 2:1); false speakers, that is, liars (1 Timothy 4:2); and false Christs (Matthew 24:24), testable (1 John 4:1), “swindler” (Luke 18:11; 1 Corinthians 5:10–11; 6:10)
• Those warnings are summarized in the word translated beware in Matthew 7:15. It is not a call simply to notice or sense something, but to be on guard against it because it is so harmful. The word conveys the idea of holding the mind away. False prophets are more than wrong; they are dangerous, and we should not expose our minds to them. They pervert thinking and poison the soul. False prophets are spiritual beasts and are immeasurably more deadly than the physical ones. Both Peter and Jude call them “unreasoning animals” (2 Peter 2:12; cf. Jude 10). - masters.edu

“And now I entrust you to God and the message of his grace that is able to build you up and give you an inheritance with all those he has set apart for himself.

“I have never coveted anyone’s silver or gold or fine clothes. You know that these hands of mine have worked to supply my own needs and even the needs of those who were with me. And I have been a constant example of how you can help those in need by working hard. You should remember the words of the Lord Jesus: ‘It is more blessed to give than to receive.’” (Journey of Generosity) Acts 20:20-35