Acts 12 Commentary

Who is "Herod the king" (Acts 12:1)?
It's Herod Agrippa (also see King Herod and Archelaus).

When was "that time" (Acts 12:1) and why did he kill James?
It was the time of the Jewish persecution of the first church, during the Great Famine. Sensing that the persecution of Christians was popular with his subjects, the unscrupulous politician most likely wanted "to harass" (Acts 12:1) the church to strengthen the Jews' acceptance, if not loyalty, of his rule.

Who was "James" (Acts 12:2)?
He was the "brother of John" (Acts 12:2), who wrote the Gospel of John, and therefore was the first of Jesus' twelve apostles to be martyred.

Why did Herod Agrippa I proceed to "seize Peter also" (Acts 12:3)?
Seeing that killing one of Jesus' twelve apostles "pleased the Jews" (Acts 12:3), he was going to murder the most prominent leader of the budding church and really be feted by the Jews.

Why didn't he kill Peter upon his arrest?
Executing anyone during "the Days of Unleavened Bread" (Acts 12:3) would have violated Jewish law and therefore displeased the Jews.

What is the Days of Unleavened Bread?
It's another name for Passover. Unleavened bread is the bread that God commanded the Jews to eat with the Passover lamb during the night when the LORD executed judgment on Egypt but passed over the homes marked by the blood of the Passover lamb, which symbolizes the blood to be shed by Jesus for our sins: "Your lamb shall be without blemish, a male of the first year. You may take it from the sheep or from the goats. Now you shall keep it until the fourteenth day of the same month. Then the whole assembly of the congregation of Israel shall kill it at twilight. And they shall take some of the blood and put it on the two doorposts and on the lintel of the houses where they eat it. Then they shall eat the flesh on that night; roasted in fire, with unleavened bread and with bitter herbs they shall eat it." (Exodus 12:5-8)

Then why was it called the "Days" (Acts 12:3) of Unleavened Bread?
God instituted it to be eaten for seven days: "So this day shall be to you a memorial; and you shall keep it as a feast to the LORD throughout your generations. You shall keep it as a feast by an everlasting ordinance. Seven days you shall eat unleavened bread. On the first day you shall remove leaven from your houses. For whoever eats leavened bread from the first day until the seventh day, that person shall be cut off from Israel. On the first day there shall be a holy convocation, and on the seventh day there shall be a holy convocation for you. No manner of work shall be done on them; but that which everyone must eat - that only may be prepared by you. So you shall observe the Feast of Unleavened Bread, for on this same day I will have brought your armies out of the land of Egypt." (Exodus 12:14-17)