There were disciples who had not heard of the Holy Spirit. Nor had they been baptized except for repentance. On both accounts Paul took immediate action to make sure the disciples were not ignorant or handicapped. I cannot imagine trying to be a disciple of Jesus without the Holy Spirit! Speaking in tongues was good authentication, not for them, but for those traveling with Paul, that they had received the real thing.
The sons of Sceva make me laugh! We know Jesus and Paul, but who are you? Ha! Then the demon beat them up and sent them away without any clothes. As a result of their folly, fear fell on everyone and the name of the Lord Jesus was magnified, a good result from a bad event.
After the book burning (5,000 pieces of silver worth!), the word increased and grew stronger according to the power of the Lord. Three different Greek words in this sentence for strength.