English Standard Version (ESV)
There's an amazing passage in Romans 2:4 that tells us that God's kindness is meant to lead us to repentance. God's aim is for us to be reconciled to him, so that our sins may be washed away and the relationship may be restored. This is God's goal.
God doesn't always use kindness, though. Sometimes, God has to confront people directly, and this is what is happening through the words of Stephen. God sent messenger after messenger to the people, but they ignored them all, so God sent Stephen to talk directly to the people, to be clear and brunt and upfront about how the people needed to change. They had enough warnings -- it was time for direct truth.
It's not that different than when kids are getting yelled at. They're surprised, but only because they've ignored the 53 different ways parents have tried to get them to change before they resorted to yelling. If they don't listen, they miss those.
In the same way, when we don't listen to God, the initial messages, the encouragements to change, don't get through. So let us be sure we set aside time to listen for what God has to say to us, that we might make the small changes before drastic changes are necessary.