Christians are called to fight sin. Sin is what Jesus died to save us from. Sin separates us from a relationship with God, as well as each other. The power of Jesus’ resurrection is that sin no longer enslaves us. God has empowered us by his Spirit to fight back against it.
For the most part, Christians have a broad agreement about what constitutes as “sin.” For example, violence, rage, greed, lust, lying, and theft are all things that Christians almost universally agree are unequivocally wrong.
Nevertheless, there are a number of other practices where less agreement exists. In some instances, scriptural support for a given action being a “sin” may be scant, but it appears to be related to or approaching other sins where we do have clear scriptural instruction.
In these instances, Christians are called to exercise wisdom — to remain above reproach and not unnecessarily put ourselves in a position to be tempted. Read more here.