Why is the Eucharist so important? Let's go to the book of Hebrews to find out.
First, St Paul says:
25 Let us not neglect our church meetings,
We call that the Mass. He says, don't neglect to meet together for the Mass. Why? He'll tell us next.
as some people do, but encourage and warn each other, especially now that the day of his coming back again is drawing near.
Apparently, people were already skipping out on the Mass, back then.
26 If anyone sins deliberately by rejecting the Savior after knowing the truth of forgiveness, this sin is not covered by Christ’s death; there is no way to get rid of it.
Then he says that neglecting to meet together for the Mass is the same thing as rejecting Christ's sacrifice. It amounts to a deliberate sin against Christ.
This is why missing the Mass is considered a mortal sin in the Catholic Church.
27 There will be nothing to look forward to but the terrible punishment of God’s awful anger, which will consume all his enemies.
Those who miss the Mass are considered God's enemies and can be certain that they will be punished for their ingratitude.
28 A man who refused to obey the laws given by Moses was killed without mercy if there were two or three witnesses to his sin. 29 Think how much more terrible the punishment will be for those who have trampled underfoot the Son of God and treated his cleansing blood as though it were common and unhallowed,...
There's the answer! Why is the Eucharist so important? Because it is the Body and Blood of Christ.
Why is missing the Mass considered to be a trampling underfoot of the Son of God?
Because it is offering of the Body of Christ which hung on the Cross for the forgiveness of our sins.
Why is it considered to be an insult to the cleansing blood of Christ?
Because it is truly the offering of the Blood of Christ which was shed for our salvation.
Notice how he compares the Old Testament gathering to the New. Saying that the New Testament gathering truly offers the Body and Blood of our Lord. Thus, to miss the Mass is no trivial thing.
Let's go to 1 Cor 11:27 So if anyone eats this bread and drinks from this cup of the Lord in an unworthy manner, >he is guilty of sin against the body and the blood of the Lord. 28 That is why a man should examine himself carefully before eating the bread and drinking from the cup. 29 For if he eats the bread and drinks from the cup unworthily, not thinking about the body of Christ and what it means, he is eating and drinking God’s judgment upon himself; for he is trifling with the death of Christ. 30 That is why many of you are weak and sick, and some have even died.
Back to Hebrews 10:29...
...and insulted and outraged the Holy Spirit who brings God’s mercy to his people.
It is such a wicked sin that St. Paul virtually equates it with the blasphemy of the Holy Spirit:
Mark 3:28 “I solemnly declare that any sin of man can be forgiven, even blasphemy against me; 29 but blasphemy against the Holy Spirit can never be forgiven. It is an eternal sin.”
30 For we know him who said, “Justice belongs to me; I will repay them”; who also said, “The Lord himself will handle these cases.” 31 It is a fearful thing to fall into the hands of the living God.
Yes, the Mass is so important that willfully missing it turns us into God's enemies. Please, inform those whom you love. Do not neglect the Mass. Because doing so is to insult the Body and Blood of the Lord.