The prison for prison, A.V.; earnestly for without ceasing, A.V. ( ἐκτενὴς, or as in the R.T. ἐκτενῶς, has the sense of intensity rather than duration; see Luke 22:14, T.R.; 1 Peter 1:22; 1 Peter 4:8).
As the last of the days of unleavened bread approached, the prayers of the Church would be more and more intense in their earnestness. We have but to read the preceding chapters to judge how precious to the Church the life of Peter must have been.