In these verses, Stephen was preaching to the Jewish leaders the history of Israel, from Abraham to Isaac, to Joseph, to Moses and so on. He kept emphasizing the fact that Israel always seemed to reject God's true witness. Stephen mentioned in v51 that they “always resist the Holy Spirit”. They did not allow God to cut away the carnality of their inner being. They would not allow God to speak to them through His messengers. They were self-righteous and self-sufficient.
Today, we can resist the Holy Spirit by rejecting what He has revealed, ignoring what He has said, and disobeying His commands. We are resisting Him when we close our ears to what He has to say because we find it offensive. Everything the Holy Spirit reveals to us is true. We must approach God's Word with a heart that submits to its authority, a heart that wants to know "the mind of the Spirit," and a heart that wants to conform to what the Spirit says. Let us not be people who are stiffnecked and would not bow to humble situations, people who are uncircumcised in heart and ears who can’t hear the spiritual truths, and people who follow our ancestors’ bad example that will adversely affect the way we believe and practice.
If you are resisting the Holy Spirit today, repent and put your trust in Christ. He never disappoints and He certainly knows what is best for us. When God calls, there is no valid excuse. God said that there is a limit to his pleading with us (Gen 6:3).