Why don't Catholics eat meat on Friday's during Lent?

Today, abstaining applies to all Catholics 14 and older and means that they must not eat meat on Ash Wednesday and all Fridays during Lent. Fasting applies to all Catholics ages 15 to 59 and means that they must eat only one full meal on Ash Wednesday and Good Friday, which means no snacks between meals. However, two smaller meals can be eaten in addition to the one full meal.

Before Vatican II, every Friday of the year - Lent or not - was a day of abstinence from meat. Today, in most countries, only Fridays in Lent are obligatory, but the Church highly recommends abstinence on Fridays during the rest of the year to show respect for the day Christ died and sacrificed his flesh on the cross. The Church also recommends that if Catholics don't abstain on Fridays outside of Lent, they should do some small form of penance or work of mercy, nevertheless.

From the book, Catholicism for Dummies by Trigilio and Brighenti

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