Leviticus 16:29-31 And this shall be statute for ever unto you: that in the seventh month, on the tenth day of the month, ye shall afflict your souls, and do no work at all. Whether it be one of your own country, or a stranger that sojourneth among you: for on that day shall the priest make an atonement for you, to cleanse you, that you may be clean from all your sins before the Lord. It shall be a sabbath of rest unto you, and ye shall afflict your souls, by a statute for ever.
The tenth day of the seventh month, ten days after Rosh Hashanah, the liturgical New Year, was the Day of Atonement (usually in October). It was a solemn Holy Day, treated as a sabbath of rest. It could be observed with fasting as an outward sign of inward penitence. But that was not required. What was commanded was to afflict your souls. Inner affliction is the commanded response to the grace and forgiveness of God.
Self-flagellation, fasting, wearing a hair shirt, doing penance, or bodily suffering is completely unnecessary, for Jesus already suffered all the painful suffering as punishment for our sins. No more sacrifice is needed. Jesus did it all. However, afflicting the soul is a helpful response for us to believe, receive, and appreciate the unlimited grace and undeserved favor of God. Afflicting the soul is honest soul-searching, genuine sorrow for sin, and sincere repentance. It involves confession of specific sins which the Spirit reveals to us. It is humbling ourselves to realize that we are not as good as we think we are. It is seeing my sin as God sees it. It is admitting that I really am a miserable sinner, full of darkness and death.
After fully afflicting the soul, we will the more firmly believe in Christ, more greatly appreciate what He has done, receive a stronger sense of release, relief, and refreshment, and let the peace and joy of the Gospel flood the soul. Afflicting the soul is letting the Law and the Gospel do its complete work in us. Weekly Worship with Communion affords the opportunity to genuinely afflict the soul, be forgiven, and feel refreshed.