Acts 12:12

συνιδών τε, and when he comprehended the matter, i.e. had taken in all the circumstances and decided what was best to be done. The same word is used (Acts 14:6) of the disciples getting news of an intended attack, and making up their minds to flee before it took place.

Μαρίας τῆς μητρὸς Ἰωάννου κ.τ.λ., Mary the mother of John, whose surname was Mark. This Mary was the sister to Barnabas as we learn in Colossians 4:10, where Mark is called sister’s son to Barnabas. This relationship accounts for the way in which the uncle clung to his nephew, even when St Paul declined to have Mark as a companion on their second proposed missionary journey. We do not read of the father of Mark anywhere, so it is probable that Mary was a widow, and, like her brother, was possessed of means which enabled her to put a house, or a part thereof, at the service of the Church, as a meeting-place for prayer.

συνηθροισμένοι καὶ προσευχόμενοι, gathered together and praying. Probably Mary’s house was a regular place for Christian assemblies. At one time they would meet for one purpose, at another for another, but just when Peter was delivered their object in meeting had been to make supplication for his deliverance.