Self-preservation is the first law of nature, but self-sacrifice is the highest rule of grace

If a commission by an earthly king is considered a honor, how can a commission by a Heavenly King be considered a sacrifice?

(Isaiah 58:1-9)
Thus says the Lord GOD:
Cry out full-throated and unsparingly,
lift up your voice like a trumpet blast;
Tell my people their wickedness,
and the house of Jacob their sins.
They seek me day after day,
and desire to know my ways,
Like a nation that has done what is just
and not abandoned the law of their God;
They ask me to declare what is due them,
pleased to gain access to God.
"Why do we fast, and you do not see it?
afflict ourselves, and you take no note of it?"

Lo, on your fast day you carry out your own pursuits,
and drive all your laborers.
Yes, your fast ends in quarreling and fighting,
striking with wicked claw.
Would that today you might fast
so as to make your voice heard on high!
Is this the manner of fasting I wish,
of keeping a day of penance:
That a man bow his head like a reed
and lie in sackcloth and ashes?
Do you call this a fast,
a day acceptable to the LORD?
This, rather, is the fasting that I wish:
releasing those bound unjustly,
untying the thongs of the yoke;
Setting free the oppressed,
breaking every yoke;
Sharing your bread with the hungry,
sheltering the oppressed and the homeless;
Clothing the naked when you see them,
and not turning your back on your own.
Then your light shall break forth like the dawn,
and your wound shall quickly be healed;
Your vindication shall go before you,
and the glory of the LORD shall be your rear guard.
Then you shall call, and the LORD will answer,
you shall cry for help, and he will say: Here I am!

Why do we fast for Lent?

Do we fast because Jesus has told us that, along with prayer, it is the most effective weapon against the kingdom of darkness? (Gospel of Life, 100)

In the reading, God chastises his people for making such a display of their fasting while at the same time mistreating their employees and fighting amongst themselves. He wants them to make their fast a time to forgive others, feed the hungry, and care for those who are hurting.

This is a time for us to renew our commitment to finding God in others by providing food for the homeless, speaking out against capital punishment, donating our time and love to a child in need. It is also closer to home that God calls us to find him, in those we live and work with such as the boss who we think is unjust, the family member who seems to annoy us on purpose, the lonely neighbor, etc.

Every year, the Holy Father John Paul II wrote us a message for Lent. One of these messages, under the motto «There is more happiness in giving than there is in receiving» (Acts 20:35); helped us to discover the very same charitable dimension of our fasting, which, from the bottom of our heart, allows us to prepare for Easter Time, in an effort to identify ourselves, more and more, with Christ's love which took him to die on the Cross for us. In short, «what every Christian ought to do all the time, he ought to do it now more carefully and more devotedly» (Saint Leo the Great, pope).