John Calvin Commentary Acts 9:28

"And he was with them going in and going out at Jerusalem," — Acts 9:28 (ASV)

Luke later says that Paul went in and out with the disciples, a phrase that signifies familiarity among the Hebrews, just as the inhabitants of cities are said to go in and out through the city gates. Therefore, after Paul was commended by Barnabas's testimony, he began to be considered one of the flock, so that he might be fully known to the Church.

Luke says again that he spoke boldly in the name of the Lord, by which words he commends his courage and steadfastness in professing the gospel. For he would never have dared to whisper amidst so many hindrances unless he had been equipped with exceptional steadfastness. Nevertheless, all men are taught what they ought to do; namely, every man according to the measure of his faith.

For though not all are Pauls, yet the faith of Christ ought to produce such great boldness in our minds that we are not entirely silent when we need to speak. I understand the name of the Lord in this passage to mean the profession of the gospel; in this sense, that Paul courageously defended Christ’s cause.