For the peace of mind and soul, we must be an upright and innocent person.

It means to be down-to-earth and be an upright and kind person who doesn't violate his conscience, so that he won't feel uneasy about his conscience and get peace of mind.

In my opinion, the only way is to abandon sin, overcome many bad habits, love and live a good, loving and forgiving life, and gain real peace and joy of mind and soul in the Lord Jesus.