The Pulpit Commentary on Acts 16:5

So for and so, A.V.; the Churches were strengthened for were the Churches established, A.V. In number; i.e. in the number of their members (comp. Acts 2:47; Acts 5:14; Acts 6:7; Acts 11:21). For the phrase, ἐστερεοῦντο τῇ πίστει, "They were made firm in the faith," comp.

Colossians 2:5, τὸ στερέωμα τῆς εἰς χριστὸν πίστεως ὑμῶν, "The steadfastness of your faith." The word is used in its physical sense in Acts 3:7, ἐστερεώθησαν αὐτοῦ αἱ βάσεις κ. τ. λ., "His feet and anklebones received strength," became fast and firm instead of being loose and vacillating.