Watchman Nee emphasizes that Christians have an opponent, Satan, who is our adversary as described in 1 Peter 5:8. He explains that this enmity began in the Garden of Eden and continues as Satan opposes believers, seeking to oppress and falsely accuse them. Nee highlights the importance of recognizing this spiritual battle and understanding that, as followers of Christ, we are aligned with Him against our common enemy. He warns that many Christians are unaware of the ongoing accusations and suffering inflicted by the devil, which must be addressed for true victory. The sermon calls believers to seek justice from God against their adversary.