This is what the Catechism of the Catholic Church states. 

 1356 If from the beginning Christians have celebrated the Eucharist and in a form whose substance has not changed despite the great diversity of times and liturgies, it is because we know ourselves to be bound by the command the Lord gave on the eve of his Passion: "Do this in remembrance of me."¹⁸³

1357 We carry out this command of the Lord by celebrating the memorial of his sacrifice. In so doing, we offer to the Father what he has himself given us: the gifts of his creation, bread and wine which, by the power of the Holy Spirit and by the words of Christ, have become the body and blood of Christ. Christ is thus really and mysteriously made present.

1358 We must therefore consider the Eucharist as:

- thanksgiving and praise to the Father;
- the sacrificial memorial of Christ and his Body;

- the presence of Christ by the power of his word and of his Spirit. 

We seek to understand mystery, but it will still remain mystery. How can we adequately thank and praise God for all he has done for us, especially for our salvation? On our own we cannot, but God provides. When we do what Jesus said and did at the Las Supper, our praise and thanksgiving is Jesus' gift to the Father on our behalf. The gift is his eternal sacrifice made present in this moment of time. How privilege are we to offer with Jesus the sacrifice and gift that is perfectly pleasing and acceptable to the Father in the Spirit! How can one ever think of being absent? How can anyone think of this celebration as a burden or something unimportant?