Catholics, like most Protestants, believe that people are saved not by works or by faith but by God’s grace.
According to the Catechism of the Catholic Church, “no one can merit the initial grace of forgiveness and justification” and “justification [being ‘declared righteous’ in Jehovah’s Witness terms] comes from the grace of God.” They define “grace” or “underserved kindness” as something more specific than the Watchtower does, a literal saving action on God’s behalf, not merely “favor” but “the free and underserved help that God gives.”—CCC 1996, 2010.
Catholic apologist Amy Welborn in her “Prove It” series for young Catholics states: “The Catholic Church teaches that, yes, we are saved by grace alone, but we’re not saved by faith alone.” She states that Catholics don’t believe that they can be unresponsive to God’s grace or help, but need to “cooperate with that grace…to grow in holiness and become more like that Divine Image” found in Christ.—Prove It! Church by Amy Welborn, Our Sunday Visitor Publishing, ISBN 0-87973-981-9.
So Catholics don’t believe that one can work to gain God’s grace. They believe one must respond to it in faith, true, just as a starving person must eat if brought food to survive, but they don't believe they can save themselves, even by their actions. Even works of merit, such as the “faith without works is dead” of the book of James is seen only possible by God’s saving help or “grace.” As one of their saints, Augustine of Hippo, wrote: “Man does not work any good things apart from God, since it is from God man receives the power to do the good things he does.”—Two Letters Against the Pelagians.
However, one does sin if they are free to observe a Church law on abstaining or a law on fasting and they refuse to do so because such laws are only active on days when the entire Church is in a formal state of penance (such as on Good Friday). Only health considerations, old age, or the lack of any other type of food or some like emergency excuses a Catholic in such situations.
A bishop may make an exception during Lent for Catholics to observe a feast day of a saint, which is supposed to be a day of celebrating Christ’s victory over evil in the example of his faithful servants. St. Patrick’s Day is such a popular feast day that always lands during Lent (the 40 days of Church-wide penance, minus Sundays, prior to Easter). Such an exemption is based on local popularity of the saint and thus at the discretion of the bishop over an area.
Certain days of the Catholic liturgical calendar should never be days of fasting or abstinence, even if they occur during formal penance times such as Lent. Solemnities such as Sabbaths (Sundays, the days of Easter and the first eight of the “twelve days” of Christmas, All Saints Day, etc.) and certain other feasts fall under such days where penance is contrary to the law to celebrate.—See Nehemiah 8:9-12.