Because the apostles were sustained by the Holy Spirit, they were strong enough to confront verbal attacks. They continued to preach the good news that God's grace was for both Gentiles and Jews.
boldly: The book of Acts often shows how the Holy Spirit gave courage to Christians (see 2:14; 4:9–10, 13; 7:2–53; 8:30–35; 9:27–28; 18:26; 19:8; 22:3–21; 23:1–6; 28:16–20, 23–31).
The Holy Spirit also affirmed the Christian message with signs and wonders (compare 5:12–16; 15:12; 16:18; 19:11).