Now, you may be asking yourself, "What does the Eucharist have to do with Thanksgiving?" Well, the word "eucharist" come from the Greek word that means, "thanksgiving." In Jn 6:11, before Christ multiplied the loaves and the fishes (an act that prefigures the Eucharistic feast), He "gave thanks" (eucharisteo). At the Last Supper, when He instituted the Eucharist, He "gave thanks" (eucharisteo) before He turned the bread and wine into His own Body, Blood, Soul, and Divinity (cf. Mt 26:27; Mk 14:23; Lk 22:17,19).
We use this word to refer to the Body of Christ that we receive in Holy Communion because it is in every way a moment of thanksgiving: It is Jesus thanking the Father:
- for those of us who the Father has given Him to be united to Him through reception of the Eucharist, and
- for the opportunity to perform the miracle that brings Him glory.
It is with a spirit of thanksgiving for all that God has given us that we offer the bread and wine that will become the Eucharist. Of course, we can't help but also thank Him for coming to dwell within us in such a profound way. That our Lord and Savior would come to be in our presence, veiled by bread and wine, and abide in us in a substantial way is a gift unlike any other. And so, on Thanksgiving, when we are to call to mind all that we are thankful for, we should not forget that which is the very meaning of "thanksgiving."
The Catechism is clear on the connection between the Eucharist and the virtue of thanksgiving:
1350 The presentation of the offerings (the Offertory). Then, sometimes in procession, the bread and wine are brought to the altar; they will be offered by the priest in the name of Christ in the Eucharistic sacrifice in which they will become his body and blood. It is the very action of Christ at the Last Supper - "taking the bread and a cup." "The Church alone offers this pure oblation to the Creator, when she offers what comes forth from his creation with thanksgiving" (St. Irenaeus, Adv. haeres. 4,18,4; cf. Mal 1:11). The presentation of the offerings at the altar takes up the gesture of Melchizedek and commits the Creator's gifts into the hands of Christ who, in his sacrifice, brings to perfection all human attempts to offer sacrifices.
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.
Thanksgiving and praise to the Father
1359 The Eucharist, the sacrament of our salvation accomplished by Christ on the cross, is also a sacrifice of praise in thanksgiving for the work of creation. In the Eucharistic sacrifice the whole of creation loved by God is presented to the Father through the death and the Resurrection of Christ. Through Christ the Church can offer the sacrifice of praise in thanksgiving for all that God has made good, beautiful, and just in creation and in humanity.
1360 The Eucharist is a sacrifice of thanksgiving to the Father, a blessing by which the Church expresses her gratitude to God for all his benefits, for all that he has accomplished through creation, redemption, and sanctification. Eucharist means first of all "thanksgiving."
1361 The Eucharist is also the sacrifice of praise by which the Church sings the glory of God in the name of all creation. This sacrifice of praise is possible only through Christ: he unites the faithful to his person, to his praise, and to his intercession, so that the sacrifice of praise to the Father is offered through Christ and with him, to be accepted in him.
To summarize, again from the Catechism:
1407 The Eucharist is the heart and the summit of the Church's life, for in it Christ associates his Church and all her members with his sacrifice of praise and thanksgiving offered once for all on the cross to his Father; by this sacrifice he pours out the graces of salvation on his Body which is the Church.
1408 The Eucharistic celebration always includes: the proclamation of the Word of God; thanksgiving to God the Father for all his benefits, above all the gift of his Son; the consecration of bread and wine; and participation in the liturgical banquet by receiving the Lord's body and blood. These elements constitute one single act of worship.
I realize that the secular holiday has Protestant roots (at least by the popular reckoning), but there's no reason why Catholics can't use this day to call to mind what they are the most thankful for: our Eucharistic Lord.