Lent is the holiest of the annual fasts and it's days are the holiest of all the days of the year. We may call it our Masters Fast because Jesus Christ fasted it.

It is a period of spiritual storing up for the whole year. He who does not spiritually benefit from it will hardly benefit from the less spiritual days.

The church allocates so much importance to this fast, and it calls it lent which means "Great" fast. It is great because of it's duration and sanctity, as it commemorates Christs sacred suffering.

That is why a sin commited during lent is most horrible. It is true that a sin is a sin, but it is more horrible during Lent than during normal days because he who sins during any fast in general, and during Lent in particular, is actually commiting a double sin: ie, the ugliness of the sin itself, in addition to the contempt shown for the holiness of those days. Therefore they are 2 sins, not one.

The point is that, in fasting, we are in need of seriousness and spirituality for we should not pursue the matter in a routine or careless manner.

From The Spirituality of Fasting