‘Now about that time Herod the king put forth his hands to afflict certain of the church.'
Note Luke's description of him as ‘the king'. It was, of course strictly correct, but here it draws out that Israel now have a king.
Herod Agrippa was a lover of Jerusalem, and ‘about that time', around the time that the Gentiles began to collect in order to meet the needs of the churches of Judaea, he determined that he would purify Jerusalem. It was at the time of the Passover, and he took the opportunity it afforded as the festal crowds gathered to ‘mistreat' the Christians in Jerusalem in order to gain popularity. He set himself against ‘certain of the church'. It may well be that in the end James was his first and only victim, although that was certainly not originally his intention. It would not be difficult to find James. The leaders of the church were prominent enough to be well known, they were not in hiding and they were caught unprepared. But whatever was the case James was arrested, and the church reeled.
‘About that time.' This happened just when things appeared to be becoming brighter because of the love and generosity of the church in Syrian Antioch which they knew would soon be coming their way. It must thus have come as a great blow to the church in Jerusalem who had probably thought that persecution was behind them.
However it may be that it is just a rough time indicator, for the events in chapter 12 take place in 44 AD whereas the visit of Barnabas and Saul may well have been in 46 AD, although preparation for the latter would have commenced earlier.