What does Acts 10:21 mean?

The Holy Spirit has told Peter about men at the gate of the house where he is staying. Peter is to "accompany them without hesitation" because the Holy Spirit sent them (Acts 10:20). "Without hesitation" may not just be a time-based command. The Greek phrasing of this can also imply that Peter is not to resist this command. He is to follow them without arguing, no matter who they are. Peter doesn't know who they are, or why they are there, though the Roman soldier is probably in uniform. He doesn't know the men will ask him to go to Caesarea to a centurion who seeks a relationship with the Jewish God. He just knows what the Holy Spirit has told him, and so he obeys.

Peter's admission, "I am the one you are looking for" is quite different from his response to others years before. While Jesus was being questioned and beaten by the Jewish leadership, Peter denied his identity and his association with Jesus (Mark 14:53–72). Now, he is going downstairs to meet with a Roman soldier who is probably wearing a similar uniform to the soldiers who beat and crucified Jesus then threw lots for Jesus' clothes (John 19).

Direct speech from the Holy Spirit is rare these days, but we can hear from God daily. The Bible is His Word to us. It contains so much of what we need to know—yet too many times it seems easy for us to ignore it. Peter heard what God wanted of him because he had a specific role in the development of the church, and because he acted faithfully when God gave him instructions in the past. In a similar way, if we are faithful with what we know God wants, He will communicate with us more, in large part by helping us understand what His Word means. But if we cannot be faithful with the little God has already given us, it's unlikely He'll give us much more (Matthew 25:21).