Say what you have seen

Notice what Peter and John are actually forbidden to do. Not to preach in general - to speak "in the name of Jesus." That is the specific thing the council wants stopped, because Peter has just said there is no other name under heaven given among men by which we must be saved.
And notice what the council could not explain. These were uneducated, common men, and Luke records the conclusion the authorities reached: "they recognized that they had been with Jesus." The boldness was not training. It was proximity.
Scripture links:
- Acts 4:12 - "there is no other name under heaven given among men by which we must be saved."
- Acts 4:13 - "they recognized that they had been with Jesus."
- Acts 4:19-20 - "we cannot but speak of what we have seen and heard."
You do not need to be impressive. You need to have been with him, and then say what you saw.