William Burkitt on Acts 12:1

Observe here, 1. Satan, the grand enemy of the church of God, never wants instruments for carrying on his persecuting designs against the church; he had many Pharaohs in the Old Testament times, bitter oppressors of the Jewish church; and several Herods under the New Testament; as Herod Antipas, and Herod Agrippa, who were very warm in the worst works, namely, that of persecution. "Herod stretched forth his hands to vex certain of the church;" that is, to kill some, and to imprison others.

Satan's bloodhounds have such an insatiable thirst after the blood of the saints that they can never be satiated with it, nor satisfied without it. A tyrannical persecutor is like an hydropic person, the more he drinks, the more he thirsts.