This verse is one of several in Acts that describe how the church grew in numbers and in faithfulness (see also 2:41; 4:4; 5:14; 6:1, 7; 12:24; 21:20).
The first Christians were learning an important truth: “The fear of the LORD is the beginning of wisdom.” This means that true knowledge starts with honoring and respecting God (Proverbs 1:7; 9:10; compare Job 28:28; Psalm 111:10; Ecclesiastes 12:13; see Luke 7:16).
As they learned to honor God, they grew stronger in their faith. Their reverence for the Lord helped the church grow (compare Acts 2:43; 19:17).