Sin
1Peter 4:3 For the time that is past suffices for doing what the Gentiles want to do, living in sensuality, passions, drunkenness, orgies, drinking parties, and lawless idolatry. 4 With respect to this they are surprised when you do not join them in the same flood of debauchery, and they malign you; 5 but they will give account to him who is ready to judge the living and the dead.
Acts 2:37 Now when they heard this they were cut to the heart, and said to Peter and the rest of the apostles, "Brothers, what shall we do?"
Peter had just finished sharing the Truth of the Gospel with the crowd and many were"cut to the heart", meaning they felt the heavy hand of conviction upon hearing the Truth. Convicted of what? The severity and consequence of their sin.