When a Christian suffers, and through that suffering finds a way of escape by their submission to God's power and purpose, the triumph of that Christian over their difficulty gives them an authority in that area, and this authority grants them the power to save many in similar circumstances. The best example of this is the Twelve Step Program for recovering alcoholics. Before these groups were started by Bill Wilson in the mid 30s, both society and the church deemed it almost impossible to save and rescue alcoholics from their destructive addiction. However, Bill was both a backslidden Christian and an alcoholic, who cried out to the Holy Spirit for help.
He then joined with another Christian alcoholic, Bob Smith, and together with God's loving guidance, they forged a healing path out of alcoholism called the Twelve Step Program. Since that time, millions of "unsavable" alcoholics have found victory in Christ as they walked on that healing path. When a recovered alcoholic speaks to another alcoholic, he/she is able to speak with a voice full of compassion, authority, strength and power, for they know EXACTLY the depths of torment and despair that another struggling alcoholic is going through. Because of their own anguished experience, a recovered Christian who has passed through alcoholism has a care, concern, eagerness and ability to communicate the good news of the gospel of Christ in the very language of the alcoholic.
Before Bill Wilson discovered the Twelve Steps of recovery, there were many different kinds of people who tried to speak the gospel of Jesus to alcoholics, but it was almost never effective enough to bring lasting deliverance and healing to the tormented addict. The reason for this is the person doing the preaching typically had no idea what kind of hell the alcoholic found themselves in, and therefore they were never able to show them the solid places upon which they could walk their way out of their torment. However, a recovered Christian is able to deliver many from all those different hells, because they themselves descended into it, and yet through Christ found a way out.