Mortification is the disciplining of the body and it's appetites by self-denial. It is a conscious effort to free our “will” from the natural inclinations of the body & mind in order to align it with the "supreme will of God".
It is not an act of doing penance; seeking to “justify”ourselves, for no work of ours is sufficient to repair the inequities we have committed against God, except the perfect sacrifice offered on the cross by Jesus.
We repeat with great desire “thy will be done on earth as it is in Heaven” many times a day. Yet it remains just a desire, unless we act with “deeds” to prove our sincerity to that desire.
As a young soldier submitting himself to rigorous training before being put into combat, we must train ourselves, cooperating with the work of the Holy Spirit with in us, to rise above our fallen nature. These deeds are not to be flaunted in the presence of men but to remain exposed only to us and to our Lord.
God supplies unlimited grace to those who endeavor. The result is “life in abundance”
For if you live according to the sinful nature, you will die; but if by the Spirit you put to death the misdeeds of the body, you will live. [Romans 8:12]