When he had considered (sunidōn). Second aorist active participle of suneidon (for the defective verb sunoraō), to see together, to grasp as a whole, old verb, but in the N.T. only here and Act 14:6, save the perfect indicative sunoida (1Co 4:4) and participle (Act 5:2). It is the word from which suneidēsis (conscience) comes (Rom 2:15). Peter’s mind worked rapidly and he decided what to do. He took in his situation clearly.
To the house of Mary (epi tēn oikian tēs Marias). Another Mary (the others were Mary the mother of Jesus, Mary of Bethany, Mary Magdalene, Mary wife of Cleopas, Mary the mother of James and Joses). She may have been a widow and was possessed of some means since her house was large enough to hold the large group of disciples there. Barnabas, cousin of John Mark her son (Col 4:10), was also a man of property or had been (Act 4:36.). It is probable that the disciples had been in the habit of meeting in her house, a fact known to Peter and he was evidently fond of John Mark whom he afterwards calls “my son” (1Pe 5:13) and whom he had met here. The upper room of Act 1:13 may have been in Mary’s house and Mark may have been the man bearing a pitcher of water (Luk 22:10) and the young man who fled in the Garden of Gethsemane (Mar 14:51.). There was a gate and portress here as in the house of the highpriest (Joh 18:16). Peter knew where to go and even at this early hour hoped to find some of the disciples. Mary is one of the many mothers who have become famous by reason of their sons, though she was undoubtedly a woman of high character herself.
Were gathered together and were praying (ēsan sunēthroisōmenoi kai proseuchomenoi). Note difference in the tenses, one periphrastic past perfect passive (sunathroizō old verb, in the N.T. here only and Act 19:25 and the uncompounded throizō in Luk 24:33) and the periphrastic imperfect. The praying apparently had been going on all night and a large number (many, hikanoi) of the disciples were there. One recalls the time when they had gathered to pray (Act 4:31) after Peter had told the disciples of the threats of the Sanhedrin (Act 4:23). God had rescued Peter then. Would he let him be put to death now as James had been?