"Wherefore I urge you to reaffirm your love for him...so that no advantage would be taken of us by Satan, for we are not ignorant of his schemes." (2 Corinthians 2:8, 11)
Paul is addressing with the Corinthians a situation in which someone has wronged the church, repented, and yet the church was not responding with the forgiveness they should have reflected. He tells them of their need to reaffirm their love for this individual. He says that failure to do so gives an advantage to the evil one.
As you go through your ministry hurt, chances are very good that a person or persons were involved in causing some or much of your pain. But now you must forgive them. If you don't, two things will surely happen. First, Satan will get an advantage in your life, in your church, in your family, and even in your ministry. And second, the advantage you give to Satan through unforgiveness will most definitely result in his attacking your mind.
Paul says, "We are not ignorant of his schemes." The word "schemes" means "mind". In other words, we are not ignorant of his "mind games." That is how Satan attacks us - through deceptive, accusatory and tempting thoughts. When we refuse to forgive we give him an advantage - a foothold into our thinking. And suddenly, we don't just think about the untrue and unbiblical thoughts he fills our mind with, we begin to believe those thoughts. And because thinking always affects our behavior, we begin to react based on our wrong thinking.
As a result, instead of acting in a way that is full of holiness, godly sincerity and the grace of God, we react out of fleshly wisdom. Unforgiveness leads to wrong thinking and wrong thinking leads to wrong behavior. Don't give Satan the advantage. Chose to forgive.