"For you have spent enough time in the past doing what pagans choose to do - living in debauchery, lust, drunkenness, orgies, carousing and detestable idolatry." NIV translation
Peter is reminding us here that we are done with all of these things. When we have had enough of carrying the burden of sin, we come to Jesus in repentance and wanting to be done with sin. If we still want to do these things, we need to check our understanding of sin and its effects.
"They think it strange that you do not plunge with them into the same flood of dissipation, and they heap abuse on you." NIV translation
Did you lose "friends" when you came to Christ? That is what is being described here as we are told that the world thinks it is strange that we do not do things that dishonor our Lord and Savior. Not only do they think we are strange but we will be persecuted because of it. We are to expect this as Jesus told us that no servant is greater than his master and they persecuted him.
"But they will have to give account to him who is ready to judge the living and the dead." NIV translation
We must keep in mind that each person will answer for their own actions. Those who do not accept Jesus as Savior and Lord will be judged and sentenced to hell. Those that have chose to accept Him as Lord and Savior will answer for what they did or did not do with the new life that He gave them. This will not be a judgment to determine where we spend eternity but a judgment of what other rewards we will receive.
"For this is the reason the gospel was preached even to those who are now dead, so that they might be judged according to men in regard to the body, but live according to God in regard to the spirit." NIV translation
This verse reminds us of the mercy of God in that Jesus even went to those that had already perished and preached the message of salvation. God does not want any people to go to hell but He is a just God and, after we hear the Word, we are responsible for it.