The second volume in Craig Keener’s magnum opus on Acts has been in for a few weeks now and I’ve been perusing it. This volume covers Acts 3:1-14:28. I found the following comments on Acts 9:31 particularly good.
“If Luke will end his entire work on a positive note (instead of Paul’s execution, Acts 28:30-31), we should not be surprised if he ends various sections positively, too, in accordance with his theme (cf. 1:8; 28:31) that nothing will stop the gospel. This verse summarizes the preceding section (on summary statements, see comment on Acts 2:41-47; 6:7); ancient speakers and writers often recapitulated the substance of what they had treated so far, sometimes long before the end of their work.
This verse serves a transitional function to the next section but is also a positive conclusion to 9:1-30. In this respect it is comparable to 12:24. In the latter case, the church has peace because God strikes the persecutor dead; in the present case, the church has peace because God converts the persecutor. God is sovereign in how he brings peace about, but in every case in Acts, persecutions are local or temporary. Devastating as they may prove to the disciples who experience them, they belong to a larger picture of God’s work in history, which ultimately prevails.” (1695)